[libcxx-commits] [libcxx] [libc++] Guard explicit ABI annotations for Clang >= 21 (PR #212249)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 requested changes to this pull request.

As https://libcxx.llvm.org/#platform-and-compiler-support states, we don't support Compilers older than Clang 21, and we in fact warn if a compiler version is used that's too old.

https://github.com/llvm/llvm-project/pull/212249