[clang] [clang-tools-extra] [llvm] [clang] Introduce diagnostics suppression mappings (PR #112517)

[Ilya Biryukov via cfe-commits]

https://github.com/ilya-biryukov commented:

I have only done a quick pass, but still wanted to leave a few NITs.

https://github.com/llvm/llvm-project/pull/112517