[clang] [clang] Don't warn on __COUNTER__ in system macros (PR #196689)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

This should come with a release note eventually but I'd like to backport this to Clang 22.x. One testing request, but I think this generally LGTM

https://github.com/llvm/llvm-project/pull/196689