[Bug libstdc++/80762] is_constructible gives hard error with clang

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80762

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |8.3

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed for GCC 8.3