[clang] [Clang][Headers] Fix tgmath.h incompatibility with Glibc (PR #161301)

[Nikolas Klauser via cfe-commits]

https://github.com/philnik777 commented:

Is there a reason to not just do `#if __has_include_next(<tgmath.h>)`?

https://github.com/llvm/llvm-project/pull/161301