[libcxx-commits] [libcxx] [libc++][NFC] Avoid using **this in error msg of std::expected (PR #84840)

[Louis Dionne via libcxx-commits]

ldionne wrote:

Rebased and used `value()` instead. I think it's clearer not to use `__val()` since that's not something users should know about.

https://github.com/llvm/llvm-project/pull/84840