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

[Fangrui Song via cfe-commits]

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@@ -0,0 +1,95 @@
+// Test that clang preincludes stdc-predef.h if we are using a libc that does
+// not pre-include it, e.g. musl.
+
+// Musl-based systems need this additional include.
+//
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MaskRay wrote:

Delete `^//$`.


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