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

[de34 at live dot cn via Gcc-bugs]

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

--- Comment #2 from Jiang An <de34 at live dot cn> ---
(In reply to Jonathan Wakely from comment #1)
> 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.

Yeah. This is perphaps in the scope of LWG484 and LWG3105, but guaranteed copy
elision doesn't seem discussed yet.