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

[Jonathan Thackray via cfe-commits]

jthackray wrote:

This is an updated version of https://reviews.llvm.org/D137043, which has been requested upstreamed by someone else within Arm, to ease porting of other software packages, and patching differences between GCC and clang.

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