[Bug libstdc++/101263] non-propagating-cache::emplace-deref missing constexpr

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101263

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #1)
> We might first need to implement P2231 (for constexpr optional) before this
> function can be properly constexpr.

Implemented in r12-4389