[libcxx-commits] [libcxx] [libc++] Remove availability annotations which can't fire anymore (PR #140049)

[Louis Dionne via libcxx-commits]

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

I'd be OK with removing the LLVM 4 annotations which are indeed not required anymore, but I'd like to retain the other ones. Keeping the macOS and iOS versions in sync is helpful for us internally to validate that versions are correct (by checking they match), and concretely leaving them here doesn't hurt.

Once we drop support for e.g. macOS 10.15, then `_LIBCPP_INTRODUCED_IN_LLVM_9` can be removed as a whole.

https://github.com/llvm/llvm-project/pull/140049