[libcxx-commits] [libcxxabi] [libc++abi] Always enable -fvisibility=hidden (PR #207333)

[Louis Dionne via libcxx-commits]

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

Assuming the output of `nm` is unchanged, I'm fine with this.

Specifically, the reason this *should* be fine is that we're already supposed to annotate all of the functions we export from libc++abi with the right ABI annotations. That's also what we already do for libc++ (where we already build with hidden visibility).

So the only potential breakage here would be if there are symbols that we export from libc++abi but we don't apply the right explicit visibility annotations to, and the `nm` check should catch that.

https://github.com/llvm/llvm-project/pull/207333