[clang] [clang][Driver] Include stdc-predef.h by default on musl (PR #202919)

[Fangrui Song via cfe-commits]

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@@ -823,6 +823,15 @@ void Linux::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
 
   if (!DriverArgs.hasArg(options::OPT_nobuiltininc) && getTriple().isMusl())
     addSystemInclude(DriverArgs, CC1Args, ResourceDirInclude);
+
+  // For GCC compatibility, add an implicit include for musl-based
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MaskRay wrote:

Both glibc and musl should have this. GCC includes this header for all glibc systems.

https://github.com/llvm/llvm-project/pull/202919