fenics-dolfinx: add missing "c" build dependency (#50071)

building fenics-dolfinx resulted in the following error:

==> No patches needed for fenics-dolfinx
==> fenics-dolfinx: Executing phase: 'cmake'
==> Error: ProcessError: Command exited with status 1:

3 errors found in build log:
     3     -- The C compiler identification is unknown
     4     -- The CXX compiler identification is GNU 12.2.0
     5     -- Detecting C compiler ABI info
     6     -- Detecting C compiler ABI info - failed
     7     -- Check for working C compiler: /opt/spack/[...]libexec/spack/cc
     8     -- Check for working C compiler: /opt/spack/[...]libexec/spack/cc - broken

  >> 9     CMake Error at /opt/spack/opt/spack/[...]/CMakeTestCCompiler.cmake:67 (message):
     10      The C compiler
     11
     12        "/opt/spack/opt/spack/[...]/libexec/spack/cc"
     13
     14      is not able to compile a simple test program.
     15

     ...

Thanks to @amd-toolchain-support issue #50021, this is easily fixed
by adding the one-liner for the missing dependency for the C compiler.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

var/spack/repos/builtin/packages/fenics-dolfinx/package.py

@@ -30,6 +30,7 @@ class FenicsDolfinx(CMakePackage):
         multi=True,
     )
 
+    depends_on("c", type="build")
     depends_on("cxx", type="build")  # generated
 
     # Graph partitioner dependencies