diff --git a/var/spack/repos/builtin.mock/packages/bowtie/package.py b/var/spack/repos/builtin.mock/packages/bowtie/package.py
index 860f646e9b6..f6bb8b41ec2 100644
--- a/var/spack/repos/builtin.mock/packages/bowtie/package.py
+++ b/var/spack/repos/builtin.mock/packages/bowtie/package.py
@@ -15,5 +15,8 @@ class Bowtie(Package):
     version("1.2.2", md5="1c837ecd990bb022d07e7aab32b09847")
     version("1.2.0", md5="1c837ecd990bb022d07e7aab32b09847")
 
+    depends_on("c", type="build")
+
     conflicts("%gcc@:4.5.0", when="@1.2.2")
-    conflicts("%gcc@:10.2.1", when="@:1.3.0")
+    conflicts("%gcc@:10.2.1", when="@:1.2.9")
+    conflicts("%gcc", when="@1.3")
diff --git a/var/spack/repos/builtin.mock/packages/callpath/package.py b/var/spack/repos/builtin.mock/packages/callpath/package.py
index 7184c15dcbb..cf3d52707f7 100644
--- a/var/spack/repos/builtin.mock/packages/callpath/package.py
+++ b/var/spack/repos/builtin.mock/packages/callpath/package.py
@@ -13,6 +13,8 @@ class Callpath(Package):
     version("0.9", md5="0123456789abcdef0123456789abcdef")
     version("1.0", md5="0123456789abcdef0123456789abcdef")
 
+    depends_on("c", type="build")
+
     depends_on("dyninst")
     depends_on("mpi")
 
diff --git a/var/spack/repos/builtin.mock/packages/cmake-client/package.py b/var/spack/repos/builtin.mock/packages/cmake-client/package.py
index c28e19518c2..c9bf018e960 100644
--- a/var/spack/repos/builtin.mock/packages/cmake-client/package.py
+++ b/var/spack/repos/builtin.mock/packages/cmake-client/package.py
@@ -29,6 +29,8 @@ class CmakeClient(CMakePackage):
     variant("single", description="", default="blue", values=("blue", "red", "green"), multi=False)
     variant("truthy", description="", default=True)
 
+    depends_on("c", type="build")
+
     callback_counter = 0
 
     flipped = False
diff --git a/var/spack/repos/builtin.mock/packages/cmake/package.py b/var/spack/repos/builtin.mock/packages/cmake/package.py
index 203b6815ad3..d32dc8bb1c9 100644
--- a/var/spack/repos/builtin.mock/packages/cmake/package.py
+++ b/var/spack/repos/builtin.mock/packages/cmake/package.py
@@ -20,6 +20,9 @@ class Cmake(Package):
     homepage = "https://www.cmake.org"
     url = "https://cmake.org/files/v3.4/cmake-3.4.3.tar.gz"
 
+    depends_on("c", type="build")
+    depends_on("cxx", type="build")
+
     version(
         "3.23.1",
         md5="4cb3ff35b2472aae70f542116d616e63",
diff --git a/var/spack/repos/builtin.mock/packages/conflict-parent/package.py b/var/spack/repos/builtin.mock/packages/conflict-parent/package.py
index 57cad8615c6..6dc3240c24c 100644
--- a/var/spack/repos/builtin.mock/packages/conflict-parent/package.py
+++ b/var/spack/repos/builtin.mock/packages/conflict-parent/package.py
@@ -14,6 +14,7 @@ class ConflictParent(Package):
     version("1.0", md5="0123456789abcdef0123456789abcdef")
 
     depends_on("conflict")
+    depends_on("c", type="build")
 
     conflicts("^conflict~foo", when="@0.9")
 
diff --git a/var/spack/repos/builtin.mock/packages/conflict/package.py b/var/spack/repos/builtin.mock/packages/conflict/package.py
index 209cd78539b..1b36c351518 100644
--- a/var/spack/repos/builtin.mock/packages/conflict/package.py
+++ b/var/spack/repos/builtin.mock/packages/conflict/package.py
@@ -17,6 +17,8 @@ class Conflict(Package):
 
     conflicts("%clang", when="+foo")
 
+    depends_on("c", type="build")
+
     def install(self, spec, prefix):
         configure("--prefix=%s" % prefix)
         make()
diff --git a/var/spack/repos/builtin.mock/packages/dt-diamond-bottom/package.py b/var/spack/repos/builtin.mock/packages/dt-diamond-bottom/package.py
index 1082bb350be..dcc6cd77eb2 100644
--- a/var/spack/repos/builtin.mock/packages/dt-diamond-bottom/package.py
+++ b/var/spack/repos/builtin.mock/packages/dt-diamond-bottom/package.py
@@ -12,3 +12,5 @@ class DtDiamondBottom(Package):
     url = "http://www.example.com/dt-diamond-bottom-1.0.tar.gz"
 
     version("1.0", md5="0123456789abcdef0123456789abcdef")
+
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/dt-diamond-left/package.py b/var/spack/repos/builtin.mock/packages/dt-diamond-left/package.py
index 682218390f1..a9337a576eb 100644
--- a/var/spack/repos/builtin.mock/packages/dt-diamond-left/package.py
+++ b/var/spack/repos/builtin.mock/packages/dt-diamond-left/package.py
@@ -14,3 +14,4 @@ class DtDiamondLeft(Package):
     version("1.0", md5="0123456789abcdef0123456789abcdef")
 
     depends_on("dt-diamond-bottom", type="build")
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/dt-diamond-right/package.py b/var/spack/repos/builtin.mock/packages/dt-diamond-right/package.py
index 9b3c42f800b..ed2b39973b3 100644
--- a/var/spack/repos/builtin.mock/packages/dt-diamond-right/package.py
+++ b/var/spack/repos/builtin.mock/packages/dt-diamond-right/package.py
@@ -14,3 +14,4 @@ class DtDiamondRight(Package):
     version("1.0", md5="0123456789abcdef0123456789abcdef")
 
     depends_on("dt-diamond-bottom", type=("build", "link", "run"))
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/dt-diamond/package.py b/var/spack/repos/builtin.mock/packages/dt-diamond/package.py
index 3774de7f932..0d60584a4f3 100644
--- a/var/spack/repos/builtin.mock/packages/dt-diamond/package.py
+++ b/var/spack/repos/builtin.mock/packages/dt-diamond/package.py
@@ -15,3 +15,5 @@ class DtDiamond(Package):
 
     depends_on("dt-diamond-left")
     depends_on("dt-diamond-right")
+
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/dyninst/package.py b/var/spack/repos/builtin.mock/packages/dyninst/package.py
index 900737dd312..5f2d1e232d9 100644
--- a/var/spack/repos/builtin.mock/packages/dyninst/package.py
+++ b/var/spack/repos/builtin.mock/packages/dyninst/package.py
@@ -28,6 +28,8 @@ class Dyninst(Package):
     depends_on("libelf")
     depends_on("libdwarf")
 
+    depends_on("c", type="build")
+
     def install(self, spec, prefix):
         mkdirp(prefix)
         touch(join_path(prefix, "dummyfile"))
diff --git a/var/spack/repos/builtin.mock/packages/fftw/package.py b/var/spack/repos/builtin.mock/packages/fftw/package.py
index 4ffb4c000d6..a169b4aa27e 100644
--- a/var/spack/repos/builtin.mock/packages/fftw/package.py
+++ b/var/spack/repos/builtin.mock/packages/fftw/package.py
@@ -18,4 +18,6 @@ class Fftw(Package):
 
     variant("mpi", default=False, description="Enable MPI")
 
+    depends_on("c", type="build")
+
     depends_on("mpi", when="+mpi")
diff --git a/var/spack/repos/builtin.mock/packages/gcc-runtime b/var/spack/repos/builtin.mock/packages/gcc-runtime
new file mode 120000
index 00000000000..6f620d9d8c2
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/gcc-runtime
@@ -0,0 +1 @@
+../../builtin/packages/gcc-runtime
\ No newline at end of file
diff --git a/var/spack/repos/builtin.mock/packages/gcc/package.py b/var/spack/repos/builtin.mock/packages/gcc/package.py
index 5aae4bae941..d054d22cf21 100644
--- a/var/spack/repos/builtin.mock/packages/gcc/package.py
+++ b/var/spack/repos/builtin.mock/packages/gcc/package.py
@@ -1,6 +1,7 @@
 # Copyright Spack Project Developers. See COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import os.path
 
 from spack.package import *
 
@@ -23,7 +24,9 @@ class Gcc(CompilerPackage, Package):
         description="Compilers and runtime libraries to build",
     )
 
-    depends_on("conflict", when="@3.0")
+    provides("c", when="languages=c")
+    provides("cxx", when="languages=c++")
+    provides("fortran", when="languages=fortran")
 
     c_names = ["gcc"]
     cxx_names = ["g++"]
@@ -33,9 +36,100 @@ class Gcc(CompilerPackage, Package):
     compiler_version_regex = r"(?<!clang version)\s?([0-9.]+)"
     compiler_version_argument = ("-dumpfullversion", "-dumpversion")
 
+    link_paths = {
+        "c": os.path.join("gcc", "gcc"),
+        "cxx": os.path.join("gcc", "g++"),
+        "fortran": os.path.join("gcc", "gfortran"),
+    }
+
     def install(self, spec, prefix):
         # Create the minimal compiler that will fool `spack compiler find`
         mkdirp(prefix.bin)
         with open(prefix.bin.gcc, "w", encoding="utf-8") as f:
             f.write('#!/bin/bash\necho "%s"' % str(spec.version))
         set_executable(prefix.bin.gcc)
+
+    @property
+    def cc(self):
+        msg = "cannot retrieve C compiler [spec is not concrete]"
+        assert self.spec.concrete, msg
+        if self.spec.external:
+            return self.spec.extra_attributes["compilers"].get("c", None)
+        result = None
+        if "languages=c" in self.spec:
+            result = str(self.spec.prefix.bin.gcc)
+        return result
+
+    @property
+    def cxx(self):
+        msg = "cannot retrieve C++ compiler [spec is not concrete]"
+        assert self.spec.concrete, msg
+        if self.spec.external:
+            return self.spec.extra_attributes["compilers"].get("cxx", None)
+        result = None
+        if "languages=c++" in self.spec:
+            result = os.path.join(self.spec.prefix.bin, "g++")
+        return result
+
+    @property
+    def fortran(self):
+        msg = "cannot retrieve Fortran compiler [spec is not concrete]"
+        assert self.spec.concrete, msg
+        if self.spec.external:
+            return self.spec.extra_attributes["compilers"].get("fortran", None)
+        result = None
+        if "languages=fortran" in self.spec:
+            result = str(self.spec.prefix.bin.gfortran)
+        return result
+
+    @classmethod
+    def runtime_constraints(cls, *, spec, pkg):
+        """Callback function to inject runtime-related rules into the solver.
+
+        Rule-injection is obtained through method calls of the ``pkg`` argument.
+
+        Documentation for this function is temporary. When the API will be in its final state,
+        we'll document the behavior at https://spack.readthedocs.io/en/latest/
+
+        Args:
+            spec: spec that will inject runtime dependencies
+            pkg: object used to forward information to the solver
+        """
+        pkg("*").depends_on(
+            "gcc-runtime",
+            when="%gcc",
+            type="link",
+            description="If any package uses %gcc, it depends on gcc-runtime",
+        )
+        pkg("*").depends_on(
+            f"gcc-runtime@{str(spec.version)}:",
+            when=f"^[deptypes=build] {spec.name}@{spec.versions}",
+            type="link",
+            description=f"If any package uses %{str(spec)}, "
+            f"it depends on gcc-runtime@{str(spec.version)}:",
+        )
+
+        gfortran_str = "libgfortran@5"
+        if spec.satisfies("gcc@:6"):
+            gfortran_str = "libgfortran@3"
+        elif spec.satisfies("gcc@7"):
+            gfortran_str = "libgfortran@4"
+
+        for fortran_virtual in ("fortran-rt", gfortran_str):
+            pkg("*").depends_on(
+                fortran_virtual,
+                when=f"^[virtuals=fortran deptypes=build] {spec.name}@{spec.versions}",
+                type="link",
+                description=f"Add a dependency on '{gfortran_str}' for nodes compiled with "
+                f"{str(spec)} and using the 'fortran' language",
+            )
+        # The version of gcc-runtime is the same as the %gcc used to "compile" it
+        pkg("gcc-runtime").requires(
+            f"@{str(spec.versions)}", when=f"^[deptypes=build] {spec.name}@{spec.versions}"
+        )
+
+        # If a node used %gcc@X.Y its dependencies must use gcc-runtime@:X.Y
+        # (technically @:X is broader than ... <= @=X but this should work in practice)
+        pkg("*").propagate(
+            f"gcc@:{str(spec.version)}", when=f"^[deptypes=build] {spec.name}@{spec.versions}"
+        )
diff --git a/var/spack/repos/builtin.mock/packages/intel-oneapi-compilers/package.py b/var/spack/repos/builtin.mock/packages/intel-oneapi-compilers/package.py
index 6524c8a7130..73849555979 100644
--- a/var/spack/repos/builtin.mock/packages/intel-oneapi-compilers/package.py
+++ b/var/spack/repos/builtin.mock/packages/intel-oneapi-compilers/package.py
@@ -26,6 +26,8 @@ class IntelOneapiCompilers(Package, CompilerPackage):
         r"(?:(?:oneAPI DPC\+\+(?:\/C\+\+)? Compiler)|(?:\(IFORT\))|(?:\(IFX\))) (\S+)"
     )
 
+    depends_on("c", type="build")
+
     @property
     def compiler_search_prefix(self):
         return self.prefix.foo.bar.baz.bin
diff --git a/var/spack/repos/builtin.mock/packages/libdwarf/package.py b/var/spack/repos/builtin.mock/packages/libdwarf/package.py
index 58558fb2b44..2ae58c15782 100644
--- a/var/spack/repos/builtin.mock/packages/libdwarf/package.py
+++ b/var/spack/repos/builtin.mock/packages/libdwarf/package.py
@@ -20,5 +20,8 @@ class Libdwarf(Package):
 
     depends_on("libelf")
 
+    depends_on("c", type="build")
+    depends_on("cxx", type="build")
+
     def install(self, spec, prefix):
         touch(prefix.libdwarf)
diff --git a/var/spack/repos/builtin.mock/packages/libelf/package.py b/var/spack/repos/builtin.mock/packages/libelf/package.py
index 90cc94df696..5fbfb45232a 100644
--- a/var/spack/repos/builtin.mock/packages/libelf/package.py
+++ b/var/spack/repos/builtin.mock/packages/libelf/package.py
@@ -15,5 +15,7 @@ class Libelf(Package):
 
     patch("local.patch", when="@0.8.10")
 
+    depends_on("c", type="build")
+
     def install(self, spec, prefix):
         touch(prefix.libelf)
diff --git a/var/spack/repos/builtin.mock/packages/llvm/package.py b/var/spack/repos/builtin.mock/packages/llvm/package.py
index 9281b6bd3b4..92dda155172 100644
--- a/var/spack/repos/builtin.mock/packages/llvm/package.py
+++ b/var/spack/repos/builtin.mock/packages/llvm/package.py
@@ -17,6 +17,8 @@ class Llvm(Package, CompilerPackage):
         "clang", default=True, description="Build the LLVM C/C++/Objective-C compiler frontend"
     )
 
+    provides("c", "cxx", when="+clang")
+
     c_names = ["clang"]
     cxx_names = ["clang++"]
     fortran_names = ["flang"]
@@ -27,3 +29,36 @@ def install(self, spec, prefix):
         with open(prefix.bin.gcc, "w", encoding="utf-8") as f:
             f.write('#!/bin/bash\necho "%s"' % str(spec.version))
         set_executable(prefix.bin.gcc)
+
+    @property
+    def cc(self):
+        msg = "cannot retrieve C compiler [spec is not concrete]"
+        assert self.spec.concrete, msg
+        if self.spec.external:
+            return self.spec.extra_attributes["compilers"].get("c", None)
+        result = None
+        if "+clang" in self.spec:
+            result = os.path.join(self.spec.prefix.bin, "clang")
+        return result
+
+    @property
+    def cxx(self):
+        msg = "cannot retrieve C++ compiler [spec is not concrete]"
+        assert self.spec.concrete, msg
+        if self.spec.external:
+            return self.spec.extra_attributes["compilers"].get("cxx", None)
+        result = None
+        if "+clang" in self.spec:
+            result = os.path.join(self.spec.prefix.bin, "clang++")
+        return result
+
+    @property
+    def fortan(self):
+        msg = "cannot retrieve Fortran compiler [spec is not concrete]"
+        assert self.spec.concrete, msg
+        if self.spec.external:
+            return self.spec.extra_attributes["compilers"].get("fc", None)
+        result = None
+        if "+flang" in self.spec:
+            result = os.path.join(self.spec.prefix.bin, "flang")
+        return result
diff --git a/var/spack/repos/builtin.mock/packages/mpich/package.py b/var/spack/repos/builtin.mock/packages/mpich/package.py
index be3e8fe4515..a6a0e049d08 100644
--- a/var/spack/repos/builtin.mock/packages/mpich/package.py
+++ b/var/spack/repos/builtin.mock/packages/mpich/package.py
@@ -26,6 +26,10 @@ class Mpich(Package):
     provides("mpi@:3", when="@3:")
     provides("mpi@:1", when="@:1")
 
+    depends_on("c", type="build")
+    depends_on("cxx", type="build")
+    depends_on("fortran", type="build")
+
     def install(self, spec, prefix):
         touch(prefix.mpich)
 
diff --git a/var/spack/repos/builtin.mock/packages/mpich2/package.py b/var/spack/repos/builtin.mock/packages/mpich2/package.py
index 48eccb30e4a..25267bef507 100644
--- a/var/spack/repos/builtin.mock/packages/mpich2/package.py
+++ b/var/spack/repos/builtin.mock/packages/mpich2/package.py
@@ -24,6 +24,8 @@ class Mpich2(Package):
     provides("mpi@:2.1", when="@1.1:")
     provides("mpi@:2.2", when="@1.2:")
 
+    depends_on("c", type="build")
+
     def install(self, spec, prefix):
         configure("--prefix=%s" % prefix)
         make()
diff --git a/var/spack/repos/builtin.mock/packages/mpileaks/package.py b/var/spack/repos/builtin.mock/packages/mpileaks/package.py
index 369972c6159..587a615cdde 100644
--- a/var/spack/repos/builtin.mock/packages/mpileaks/package.py
+++ b/var/spack/repos/builtin.mock/packages/mpileaks/package.py
@@ -24,6 +24,8 @@ class Mpileaks(Package):
     depends_on("mpi")
     depends_on("callpath")
 
+    depends_on("c", type="build")
+
     # Will be used to try raising an exception
     libs = None
 
diff --git a/var/spack/repos/builtin.mock/packages/multimethod/package.py b/var/spack/repos/builtin.mock/packages/multimethod/package.py
index 4d33aa38913..40241739a2a 100644
--- a/var/spack/repos/builtin.mock/packages/multimethod/package.py
+++ b/var/spack/repos/builtin.mock/packages/multimethod/package.py
@@ -25,6 +25,7 @@ class Multimethod(MultimethodBase):
     variant("mpi", default=False, description="")
 
     depends_on("mpi", when="+mpi")
+    depends_on("c", type="build")
 
     #
     # These functions are only valid for versions 1, 3, and 4.
@@ -79,7 +80,7 @@ def mpi_version(self):
     def has_a_default(self):
         return "default"
 
-    @when("%gcc")
+    @when("%gcc@10:")
     def has_a_default(self):
         return "gcc"
 
diff --git a/var/spack/repos/builtin.mock/packages/multivalue-variant/package.py b/var/spack/repos/builtin.mock/packages/multivalue-variant/package.py
index 5efd8fc27b6..aad64615f2d 100644
--- a/var/spack/repos/builtin.mock/packages/multivalue-variant/package.py
+++ b/var/spack/repos/builtin.mock/packages/multivalue-variant/package.py
@@ -41,3 +41,5 @@ class MultivalueVariant(Package):
     depends_on("callpath")
     depends_on("pkg-a")
     depends_on("pkg-a@1.0", when="fee=barbaz")
+
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/openblas-with-lapack/package.py b/var/spack/repos/builtin.mock/packages/openblas-with-lapack/package.py
index 8585b75d07f..0247235ffb0 100644
--- a/var/spack/repos/builtin.mock/packages/openblas-with-lapack/package.py
+++ b/var/spack/repos/builtin.mock/packages/openblas-with-lapack/package.py
@@ -14,3 +14,4 @@ class OpenblasWithLapack(Package):
     version("0.2.15", md5="b1190f3d3471685f17cfd1ec1d252ac9")
 
     provides("lapack", "blas")
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/openblas/package.py b/var/spack/repos/builtin.mock/packages/openblas/package.py
index 4da32d64cb6..23be201c4d2 100644
--- a/var/spack/repos/builtin.mock/packages/openblas/package.py
+++ b/var/spack/repos/builtin.mock/packages/openblas/package.py
@@ -18,6 +18,8 @@ class Openblas(Package):
 
     variant("shared", default=True, description="Build shared libraries")
 
+    depends_on("c", type="build")
+
     # See #20019 for this conflict
     conflicts("%gcc@:4.4", when="@0.2.14:")
 
diff --git a/var/spack/repos/builtin.mock/packages/pkg-a/package.py b/var/spack/repos/builtin.mock/packages/pkg-a/package.py
index 42e3ee18363..0d08099e936 100644
--- a/var/spack/repos/builtin.mock/packages/pkg-a/package.py
+++ b/var/spack/repos/builtin.mock/packages/pkg-a/package.py
@@ -35,6 +35,8 @@ class PkgA(AutotoolsPackage):
     depends_on("pkg-b", when="foobar=bar")
     depends_on("test-dependency", type="test")
 
+    depends_on("c", type="build")
+
     parallel = False
 
 
diff --git a/var/spack/repos/builtin.mock/packages/pkg-b/package.py b/var/spack/repos/builtin.mock/packages/pkg-b/package.py
index 570d1266879..9949ea05d71 100644
--- a/var/spack/repos/builtin.mock/packages/pkg-b/package.py
+++ b/var/spack/repos/builtin.mock/packages/pkg-b/package.py
@@ -18,4 +18,5 @@ class PkgB(Package):
         "foo", description="", values=any_combination_of("bar", "baz", "fee").with_default("bar")
     )
 
+    depends_on("c", type="build")
     depends_on("test-dependency", type="test")
diff --git a/var/spack/repos/builtin.mock/packages/pkg-c/package.py b/var/spack/repos/builtin.mock/packages/pkg-c/package.py
index dfc30311a55..18c8bb71721 100644
--- a/var/spack/repos/builtin.mock/packages/pkg-c/package.py
+++ b/var/spack/repos/builtin.mock/packages/pkg-c/package.py
@@ -11,4 +11,16 @@ class PkgC(Package):
     homepage = "http://www.example.com"
     url = "http://www.example.com/c-1.0.tar.gz"
 
+    # Needed to test CDash reporting
+    phases = ["configure", "build", "install"]
+
     version("1.0", md5="0123456789abcdef0123456789abcdef")
+
+    def configure(self, spec, prefix):
+        pass
+
+    def build(self, spec, prefix):
+        pass
+
+    def install(self, spec, prefix):
+        touch(prefix.pkg_c)
diff --git a/var/spack/repos/builtin.mock/packages/requires_clang/package.py b/var/spack/repos/builtin.mock/packages/requires_clang/package.py
index 592078fcb8e..667a5b9d3da 100644
--- a/var/spack/repos/builtin.mock/packages/requires_clang/package.py
+++ b/var/spack/repos/builtin.mock/packages/requires_clang/package.py
@@ -15,3 +15,5 @@ class RequiresClang(Package):
     version("0.9", md5="abcd456789abcdef0123456789abcdef")
 
     requires("%clang", msg="can only be compiled with Clang")
+
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/requires_clang_or_gcc/package.py b/var/spack/repos/builtin.mock/packages/requires_clang_or_gcc/package.py
index 58b2d301562..4249afdcf4d 100644
--- a/var/spack/repos/builtin.mock/packages/requires_clang_or_gcc/package.py
+++ b/var/spack/repos/builtin.mock/packages/requires_clang_or_gcc/package.py
@@ -15,3 +15,5 @@ class RequiresClangOrGcc(Package):
     version("0.9", md5="abcd456789abcdef0123456789abcdef")
 
     requires("%gcc", "%clang", policy="one_of")
+
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/simple-inheritance/package.py b/var/spack/repos/builtin.mock/packages/simple-inheritance/package.py
index f8b814ae165..c37f2253611 100644
--- a/var/spack/repos/builtin.mock/packages/simple-inheritance/package.py
+++ b/var/spack/repos/builtin.mock/packages/simple-inheritance/package.py
@@ -28,3 +28,5 @@ class SimpleInheritance(BaseWithDirectives):
 
     depends_on("openblas", when="+openblas")
     provides("lapack", when="+openblas")
+
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/sticky-variant-dependent/package.py b/var/spack/repos/builtin.mock/packages/sticky-variant-dependent/package.py
index b888dae6027..1b3188fb2ae 100644
--- a/var/spack/repos/builtin.mock/packages/sticky-variant-dependent/package.py
+++ b/var/spack/repos/builtin.mock/packages/sticky-variant-dependent/package.py
@@ -14,3 +14,5 @@ class StickyVariantDependent(AutotoolsPackage):
 
     depends_on("sticky-variant")
     conflicts("%gcc", when="^sticky-variant~allow-gcc")
+
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/sticky-variant/package.py b/var/spack/repos/builtin.mock/packages/sticky-variant/package.py
index 44568f56519..e8d3c63fc77 100644
--- a/var/spack/repos/builtin.mock/packages/sticky-variant/package.py
+++ b/var/spack/repos/builtin.mock/packages/sticky-variant/package.py
@@ -15,3 +15,5 @@ class StickyVariant(AutotoolsPackage):
     variant("allow-gcc", description="", default=False, sticky=True)
 
     conflicts("%gcc", when="~allow-gcc")
+
+    depends_on("c", type="build")
diff --git a/var/spack/repos/builtin.mock/packages/with-constraint-met/package.py b/var/spack/repos/builtin.mock/packages/with-constraint-met/package.py
index 5eac68dfcb1..1e2f6907d5c 100644
--- a/var/spack/repos/builtin.mock/packages/with-constraint-met/package.py
+++ b/var/spack/repos/builtin.mock/packages/with-constraint-met/package.py
@@ -14,6 +14,8 @@ class WithConstraintMet(Package):
     version("2.0", md5="0123456789abcdef0123456789abcdef")
     version("1.0", md5="0123456789abcdef0123456789abcdef")
 
+    depends_on("c", type="build")
+
     with when("@1.0"):
         depends_on("pkg-b")
         conflicts("%gcc", when="+foo")
diff --git a/var/spack/repos/builtin.mock/packages/zmpi/package.py b/var/spack/repos/builtin.mock/packages/zmpi/package.py
index 7fbd62e3f04..dea99f86052 100644
--- a/var/spack/repos/builtin.mock/packages/zmpi/package.py
+++ b/var/spack/repos/builtin.mock/packages/zmpi/package.py
@@ -15,4 +15,6 @@ class Zmpi(Package):
     version("1.0", md5="0123456789abcdef0123456789abcdef")
 
     provides("mpi@:10.0")
+
     depends_on("fake")
+    depends_on("c", type="build")
diff --git a/var/spack/repos/compiler_runtime.test/packages/gcc b/var/spack/repos/compiler_runtime.test/packages/gcc
new file mode 120000
index 00000000000..17e3b9e575b
--- /dev/null
+++ b/var/spack/repos/compiler_runtime.test/packages/gcc
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc
\ No newline at end of file
diff --git a/var/spack/repos/compiler_runtime.test/packages/gcc-runtime b/var/spack/repos/compiler_runtime.test/packages/gcc-runtime
new file mode 120000
index 00000000000..0e770302bf4
--- /dev/null
+++ b/var/spack/repos/compiler_runtime.test/packages/gcc-runtime
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc-runtime
\ No newline at end of file
diff --git a/var/spack/repos/compiler_runtime.test/packages/gcc-runtime/package.py b/var/spack/repos/compiler_runtime.test/packages/gcc-runtime/package.py
deleted file mode 100644
index e85021ba0ae..00000000000
--- a/var/spack/repos/compiler_runtime.test/packages/gcc-runtime/package.py
+++ /dev/null
@@ -1,12 +0,0 @@
-# Copyright Spack Project Developers. See COPYRIGHT file for details.
-#
-# SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-from spack.package import *
-
-
-class GccRuntime(Package):
-    homepage = "https://example.com"
-    has_code = False
-    tags = ["runtime"]
-    requires("%gcc")
diff --git a/var/spack/repos/compiler_runtime.test/packages/gcc/package.py b/var/spack/repos/compiler_runtime.test/packages/gcc/package.py
deleted file mode 100644
index ddd0e04852e..00000000000
--- a/var/spack/repos/compiler_runtime.test/packages/gcc/package.py
+++ /dev/null
@@ -1,34 +0,0 @@
-# Copyright Spack Project Developers. See COPYRIGHT file for details.
-#
-# SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
-from spack.package import *
-
-
-class Gcc(Package):
-    homepage = "http://www.example.com/"
-    has_code = False
-
-    version("13.2.0")
-    version("12.3.0")
-
-    @classmethod
-    def runtime_constraints(cls, *, spec, pkg):
-        pkg("*").depends_on(
-            "gcc-runtime",
-            when="%gcc",
-            type="link",
-            description="If any package uses %gcc, it depends on gcc-runtime",
-        )
-        pkg("*").depends_on(
-            f"gcc-runtime@{str(spec.version)}:",
-            when=f"%{str(spec)}",
-            type="link",
-            description=f"If any package uses %{str(spec)}, "
-            f"it depends on gcc-runtime@{str(spec.version)}:",
-        )
-        # The version of gcc-runtime is the same as the %gcc used to "compile" it
-        pkg("gcc-runtime").requires(f"@={str(spec.version)}", when=f"%{str(spec)}")
-
-        # If a node used %gcc@X.Y its dependencies must use gcc-runtime@:X.Y
-        pkg("*").propagate(f"%gcc@:{str(spec.version)}", when=f"%{str(spec)}")
diff --git a/var/spack/repos/compiler_runtime.test/packages/glibc b/var/spack/repos/compiler_runtime.test/packages/glibc
new file mode 120000
index 00000000000..f9cd337cc24
--- /dev/null
+++ b/var/spack/repos/compiler_runtime.test/packages/glibc
@@ -0,0 +1 @@
+../../builtin.mock/packages/glibc
\ No newline at end of file
diff --git a/var/spack/repos/compiler_runtime.test/packages/gmake b/var/spack/repos/compiler_runtime.test/packages/gmake
new file mode 120000
index 00000000000..86bbc3dd35a
--- /dev/null
+++ b/var/spack/repos/compiler_runtime.test/packages/gmake
@@ -0,0 +1 @@
+../../builtin.mock/packages/gmake
\ No newline at end of file
diff --git a/var/spack/repos/compiler_runtime.test/packages/gnuconfig b/var/spack/repos/compiler_runtime.test/packages/gnuconfig
new file mode 120000
index 00000000000..cfb894494bd
--- /dev/null
+++ b/var/spack/repos/compiler_runtime.test/packages/gnuconfig
@@ -0,0 +1 @@
+../../builtin.mock/packages/gnuconfig
\ No newline at end of file
diff --git a/var/spack/repos/compiler_runtime.test/packages/pkg-a/package.py b/var/spack/repos/compiler_runtime.test/packages/pkg-a/package.py
index f467fe3a6ed..ef30c324e72 100644
--- a/var/spack/repos/compiler_runtime.test/packages/pkg-a/package.py
+++ b/var/spack/repos/compiler_runtime.test/packages/pkg-a/package.py
@@ -10,3 +10,6 @@ class PkgA(Package):
 
     version("1.0")
     depends_on("pkg-b")
+
+    depends_on("c", type="build")
+    depends_on("cxx", type="build")
diff --git a/var/spack/repos/compiler_runtime.test/packages/pkg-b/package.py b/var/spack/repos/compiler_runtime.test/packages/pkg-b/package.py
index 0bdbaacd0c1..83948af641e 100644
--- a/var/spack/repos/compiler_runtime.test/packages/pkg-b/package.py
+++ b/var/spack/repos/compiler_runtime.test/packages/pkg-b/package.py
@@ -9,3 +9,6 @@ class PkgB(Package):
     has_code = False
 
     version("1.0")
+
+    depends_on("c", type="build")
+    depends_on("cxx", type="build")
diff --git a/var/spack/repos/duplicates.test/packages/gcc b/var/spack/repos/duplicates.test/packages/gcc
new file mode 120000
index 00000000000..17e3b9e575b
--- /dev/null
+++ b/var/spack/repos/duplicates.test/packages/gcc
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc
\ No newline at end of file
diff --git a/var/spack/repos/duplicates.test/packages/gcc-runtime b/var/spack/repos/duplicates.test/packages/gcc-runtime
new file mode 120000
index 00000000000..0e770302bf4
--- /dev/null
+++ b/var/spack/repos/duplicates.test/packages/gcc-runtime
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc-runtime
\ No newline at end of file
diff --git a/var/spack/repos/duplicates.test/packages/glibc b/var/spack/repos/duplicates.test/packages/glibc
new file mode 120000
index 00000000000..f9cd337cc24
--- /dev/null
+++ b/var/spack/repos/duplicates.test/packages/glibc
@@ -0,0 +1 @@
+../../builtin.mock/packages/glibc
\ No newline at end of file
diff --git a/var/spack/repos/duplicates.test/packages/gnuconfig b/var/spack/repos/duplicates.test/packages/gnuconfig
new file mode 120000
index 00000000000..cfb894494bd
--- /dev/null
+++ b/var/spack/repos/duplicates.test/packages/gnuconfig
@@ -0,0 +1 @@
+../../builtin.mock/packages/gnuconfig
\ No newline at end of file
diff --git a/var/spack/repos/duplicates.test/packages/llvm b/var/spack/repos/duplicates.test/packages/llvm
new file mode 120000
index 00000000000..7dddef3a960
--- /dev/null
+++ b/var/spack/repos/duplicates.test/packages/llvm
@@ -0,0 +1 @@
+../../builtin.mock/packages/llvm
\ No newline at end of file
diff --git a/var/spack/repos/edges.test/packages/gcc b/var/spack/repos/edges.test/packages/gcc
new file mode 120000
index 00000000000..17e3b9e575b
--- /dev/null
+++ b/var/spack/repos/edges.test/packages/gcc
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc
\ No newline at end of file
diff --git a/var/spack/repos/edges.test/packages/gcc-runtime b/var/spack/repos/edges.test/packages/gcc-runtime
new file mode 120000
index 00000000000..0e770302bf4
--- /dev/null
+++ b/var/spack/repos/edges.test/packages/gcc-runtime
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc-runtime
\ No newline at end of file
diff --git a/var/spack/repos/edges.test/packages/glibc b/var/spack/repos/edges.test/packages/glibc
new file mode 120000
index 00000000000..f9cd337cc24
--- /dev/null
+++ b/var/spack/repos/edges.test/packages/glibc
@@ -0,0 +1 @@
+../../builtin.mock/packages/glibc
\ No newline at end of file
diff --git a/var/spack/repos/edges.test/packages/gmake b/var/spack/repos/edges.test/packages/gmake
new file mode 120000
index 00000000000..86bbc3dd35a
--- /dev/null
+++ b/var/spack/repos/edges.test/packages/gmake
@@ -0,0 +1 @@
+../../builtin.mock/packages/gmake
\ No newline at end of file
diff --git a/var/spack/repos/edges.test/packages/gnuconfig b/var/spack/repos/edges.test/packages/gnuconfig
new file mode 120000
index 00000000000..cfb894494bd
--- /dev/null
+++ b/var/spack/repos/edges.test/packages/gnuconfig
@@ -0,0 +1 @@
+../../builtin.mock/packages/gnuconfig
\ No newline at end of file
diff --git a/var/spack/repos/edges.test/packages/llvm b/var/spack/repos/edges.test/packages/llvm
new file mode 120000
index 00000000000..7dddef3a960
--- /dev/null
+++ b/var/spack/repos/edges.test/packages/llvm
@@ -0,0 +1 @@
+../../builtin.mock/packages/llvm
\ No newline at end of file
diff --git a/var/spack/repos/flags.test/packages/gcc b/var/spack/repos/flags.test/packages/gcc
new file mode 120000
index 00000000000..17e3b9e575b
--- /dev/null
+++ b/var/spack/repos/flags.test/packages/gcc
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc
\ No newline at end of file
diff --git a/var/spack/repos/flags.test/packages/gcc-runtime b/var/spack/repos/flags.test/packages/gcc-runtime
new file mode 120000
index 00000000000..0e770302bf4
--- /dev/null
+++ b/var/spack/repos/flags.test/packages/gcc-runtime
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc-runtime
\ No newline at end of file
diff --git a/var/spack/repos/flags.test/packages/glibc b/var/spack/repos/flags.test/packages/glibc
new file mode 120000
index 00000000000..f9cd337cc24
--- /dev/null
+++ b/var/spack/repos/flags.test/packages/glibc
@@ -0,0 +1 @@
+../../builtin.mock/packages/glibc
\ No newline at end of file
diff --git a/var/spack/repos/flags.test/packages/gmake b/var/spack/repos/flags.test/packages/gmake
new file mode 120000
index 00000000000..eefeb5e47f5
--- /dev/null
+++ b/var/spack/repos/flags.test/packages/gmake
@@ -0,0 +1 @@
+../../builtin.mock/packages/gmake/
\ No newline at end of file
diff --git a/var/spack/repos/flags.test/packages/gnuconfig b/var/spack/repos/flags.test/packages/gnuconfig
new file mode 120000
index 00000000000..cfb894494bd
--- /dev/null
+++ b/var/spack/repos/flags.test/packages/gnuconfig
@@ -0,0 +1 @@
+../../builtin.mock/packages/gnuconfig
\ No newline at end of file
diff --git a/var/spack/repos/requirements.test/packages/gcc b/var/spack/repos/requirements.test/packages/gcc
new file mode 120000
index 00000000000..17e3b9e575b
--- /dev/null
+++ b/var/spack/repos/requirements.test/packages/gcc
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc
\ No newline at end of file
diff --git a/var/spack/repos/requirements.test/packages/gcc-runtime b/var/spack/repos/requirements.test/packages/gcc-runtime
new file mode 120000
index 00000000000..0e770302bf4
--- /dev/null
+++ b/var/spack/repos/requirements.test/packages/gcc-runtime
@@ -0,0 +1 @@
+../../builtin.mock/packages/gcc-runtime
\ No newline at end of file
diff --git a/var/spack/repos/requirements.test/packages/glibc b/var/spack/repos/requirements.test/packages/glibc
new file mode 120000
index 00000000000..f9cd337cc24
--- /dev/null
+++ b/var/spack/repos/requirements.test/packages/glibc
@@ -0,0 +1 @@
+../../builtin.mock/packages/glibc
\ No newline at end of file
diff --git a/var/spack/repos/requirements.test/packages/gmake b/var/spack/repos/requirements.test/packages/gmake
new file mode 120000
index 00000000000..eefeb5e47f5
--- /dev/null
+++ b/var/spack/repos/requirements.test/packages/gmake
@@ -0,0 +1 @@
+../../builtin.mock/packages/gmake/
\ No newline at end of file
diff --git a/var/spack/repos/requirements.test/packages/gnuconfig b/var/spack/repos/requirements.test/packages/gnuconfig
new file mode 120000
index 00000000000..cfb894494bd
--- /dev/null
+++ b/var/spack/repos/requirements.test/packages/gnuconfig
@@ -0,0 +1 @@
+../../builtin.mock/packages/gnuconfig
\ No newline at end of file
diff --git a/var/spack/repos/requirements.test/packages/llvm b/var/spack/repos/requirements.test/packages/llvm
new file mode 120000
index 00000000000..7dddef3a960
--- /dev/null
+++ b/var/spack/repos/requirements.test/packages/llvm
@@ -0,0 +1 @@
+../../builtin.mock/packages/llvm
\ No newline at end of file