[clang] [clang] Don't use -Wno-nested-anon-types on GCC (PR #95029)

[Vlad Serebrennikov via cfe-commits]

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

`-Wnested-anon-types` isn't supported even by GCC 7.4, so yeah, thank you for fixing this.

https://github.com/llvm/llvm-project/pull/95029