[libcxx-commits] [libcxx] [libc++] Make `constexpr std::variant`. Implement P2231R1 (PR #83335)

[Louis Dionne via libcxx-commits]

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

This LGTM but please rebase on `main`, I made some changes to `variant` which conflict with this PR!

https://github.com/llvm/llvm-project/pull/83335