[clang] [clang-tools-extra] [clang-tidy] Avoid processing declarations in system headers (PR #128150)

[Carlos Galvez via cfe-commits]

carlosgalvezp wrote:

Ok! Will fix sometime today. I think this topic needs some more careful iteration and we should unblock.

Worth noting is that even though a lot of warnings still remain the performance gain was still significant, i.e. going from 10 seconds (baseline) to 3 seconds (proposal). Trunk takes 1 second.

https://github.com/llvm/llvm-project/pull/128150