[libcxx-commits] [libcxx] [libc++][modules] Add a header to forward-declare std::get (PR #108285)

[Louis Dionne via libcxx-commits]

ldionne wrote:

As we discussed during our 1:1, this issue is indeed caught by the existing tests when we modularized. The reason why things work right now is that `variant` is pulled into `elements_view.h` transitively via `common_iterator`. However once we modularize stuff, those declarations are not visible even though they are technically "there", and we need to properly include them.

https://github.com/llvm/llvm-project/pull/108285