[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:

> Thank you for the fix! Can you also add test coverage for the changes to `clang/test/Headers` and a release note so users know about the fix to `clang/docs/ReleaseNotes.rst`?
> 
> Also, precommit CI found relevant failures:
> 
> ```
> ******************** TEST 'Clang :: Preprocessor/init-aarch64.c' FAILED ********************
> Exit Code: 1
> Command Output (stderr):
> --
> RUN: at line 1: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/build/bin/clang -cc1 -internal-isystem /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/build/lib/clang/20/include -nostdsysteminc -E -dM -triple=aarch64 -xc /dev/null > /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/build/tools/clang/test/Preprocessor/Output/init-aarch64.c.tmp.aarch64
> + /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/build/bin/clang -cc1 -internal-isystem /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/build/lib/clang/20/include -nostdsysteminc -E -dM -triple=aarch64 -xc /dev/null
> RUN: at line 2: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/build/bin/FileCheck --check-prefixes=AARCH64,AARCH64_LE,AARCH64_C /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/clang/test/Preprocessor/init-aarch64.c --match-full-lines < /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/build/tools/clang/test/Preprocessor/Output/init-aarch64.c.tmp.aarch64
> + /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/build/bin/FileCheck --check-prefixes=AARCH64,AARCH64_LE,AARCH64_C /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/clang/test/Preprocessor/init-aarch64.c --match-full-lines
> /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/clang/test/Preprocessor/init-aarch64.c:138:18: error: AARCH64-NEXT: is not on the line after the previous match
> // AARCH64-NEXT: #define __INT16_C_SUFFIX__
>                  ^
> <stdin>:124:1: note: 'next' match was here
> #define __INT16_C_SUFFIX__
> ^
> <stdin>:122:43: note: previous match ended here
> #define __HAVE_FUNCTION_MULTI_VERSIONING 1
>                                           ^
> <stdin>:123:1: note: non-matching line after previous match is here
> #define __INT16_C(c) c
> ^
> Input file: <stdin>
> Check file: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-jfggl-1/llvm-project/github-pull-requests/clang/test/Preprocessor/init-aarch64.c
> -dump-input=help explains the following input dump.
> Input was:
> <<<<<<
>           .
>           .
>           .
>         119: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1
>         120: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1
>         121: #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 1
>         122: #define __HAVE_FUNCTION_MULTI_VERSIONING 1
>         123: #define __INT16_C(c) c
>         124: #define __INT16_C_SUFFIX__
> next:138     !~~~~~~~~~~~~~~~~~~~~~~~~~~  error: match on wrong line
>         125: #define __INT16_FMTd__ "hd"
>         126: #define __INT16_FMTi__ "hi"
>         127: #define __INT16_MAX__ 32767
>         128: #define __INT16_TYPE__ short
>         129: #define __INT32_C(c) c
>           .
>           .
>           .
> >>>>>>
> --
> ********************
> ```
> 
> (and similar in init.c)

OK, let me work on that.

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