[clang] [Clang] Add predefined macros for integer constants to implement section 7.18.4 of ISO/IEC 9899:1999 in `<stdint.h>` in a safe way (PR #123514)

[Manuel Sainz de Baranda y Goñi via cfe-commits]

redcode wrote:

@jrtc27 has explained to me that the `{{$}}` expressions in `init-v7k-compat.c` are not due to a bug, so I have updated that file as well.

https://github.com/llvm/llvm-project/pull/123514