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

[kadir çetinkaya via llvm-commits]

kadircet wrote:

gentle ping @AaronBallman, I believe you were supportive of this approach in final version of [RFC](https://discourse.llvm.org/t/rfc-add-support-for-controlling-diagnostics-severities-at-file-level-granularity-through-command-line/81292/12?u=kadircet) but I'd like to make sure this agreement was implemented in an accurate manner.

So it'd be great if you can check the overall interaction in https://github.com/llvm/llvm-project/blob/61b963131975ca3f6536b38427e25024f8759c57/clang/test/Misc/warning-suppression-mappings.cpp and https://github.com/llvm/llvm-project/blob/61b963131975ca3f6536b38427e25024f8759c57/clang/test/Misc/Inputs/suppression-mapping.txt. If those look good, I am happy to settle on the details of the implementation with other reviewers.

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