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

[Nikita Popov via cfe-commits]

nikic wrote:

Though looking at that file list in more details, this also affects files outside clang, so I think it might be adding some compile-time overhead that is only visible on specific workloads. E.g. `LLVMSupport.dir/UnicodeNameToCodepointGenerated.cpp` has a 4.5% increase.

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