[Bug libstdc++/115059] Constraints/Mandates on the comparison operators of std::optional and std::variant are overly strict

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115059

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I don't want to change anything in libstdc++ here. Either std::is_convertible
should be sufficient to check "convertible to" constraints, or "convertible to"
should exclude these kind of games.