Mac OS UUID virtual: platform-specific virtuals not correctly prioritized (#43002)

`apple-libuuid` includes types that aren't available in other `uuid`
providers; this cause issues in consuming packages (e.g., py-matplotlib)
that use SDKs like CarbonCore.framework when they attempt to use
`util-linux-uuid` as a `uuid` provider on Mac OS.

Tweak `util-linux-uuid` to indicate that it does not provide `uuid`
on Mac OS.

var/spack/repos/builtin/packages/libuuid/package.py

@@ -3,6 +3,8 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import sys
+
 from spack.package import *
 
 
@@ -20,6 +22,7 @@ class Libuuid(AutotoolsPackage, SourceforgePackage):
 
     depends_on("c", type="build")  # generated
 
-    provides("uuid")
+    if sys.platform not in ["darwin", "win32"]:
+        provides("uuid")
 
     conflicts("%gcc@14:")

var/spack/repos/builtin/packages/ossp-uuid/package.py

@@ -3,6 +3,8 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import sys
+
 from spack.package import *
 
 
@@ -22,7 +24,8 @@ class OsspUuid(AutotoolsPackage):
     depends_on("c", type="build")  # generated
     depends_on("cxx", type="build")  # generated
 
-    provides("uuid")
+    if sys.platform not in ["darwin", "win32"]:
+        provides("uuid")
 
     @property
     def libs(self):

var/spack/repos/builtin/packages/util-linux-uuid/package.py

@@ -3,6 +3,8 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import sys
+
 from spack.package import *
 
 
@@ -29,7 +31,8 @@ class UtilLinuxUuid(AutotoolsPackage):
 
     depends_on("pkgconfig", type="build")
 
-    provides("uuid")
+    if sys.platform not in ["darwin", "win32"]:
+        provides("uuid")
 
     def url_for_version(self, version):
         url = "https://www.kernel.org/pub/linux/utils/util-linux/v{0}/util-linux-{1}.tar.gz"