[Bug c++/80387] [6/7 Regression] G++ get stuck due to decltype over constexpr static function in using declaration

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80387

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
PR 80396 requests such a builtin.