[clang-tools-extra] [clang-tidy] Skip system macros in readability-identifier-naming check (PR #132016)

[Carlos Galvez via cfe-commits]

carlosgalvezp wrote:

Yes, the patch can be merged and gets rid of about half the remaining warnings in system headers! I've removed the condition about checking for the `SystemHeaders` flag, for consistency with similar code for ignoring the `Decl`s, which further simplifies the logic.

https://github.com/llvm/llvm-project/pull/132016