[compiler-rt] [NFCI] clarify that asan-*linux.cpp files affect *nix OS'es (PR #195565)

[Thurston Dang via llvm-commits]

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

Looks good to me, but please postpone merging to give Florian and Vitaly the opportunity to chime in if desired.

https://github.com/llvm/llvm-project/pull/195565