[clang-tools-extra] [clang-tidy][libc] Fix namespace check with macro (PR #68134)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL approved this pull request.

>From functional point of view looks fine, could be more strict but should still work.

https://github.com/llvm/llvm-project/pull/68134