[Bug libstdc++/71579] type_traits miss checks for type completeness in some traits

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71579

--- Comment #12 from Antony Polukhin <antoshkka at gmail dot com> ---
(In reply to Jonathan Wakely from comment #11)
> This change broke a compiler test: g++.dg/cpp0x/noexcept15.C
> 
> I'll have to figure out how to update that test to keep testing what it was
> meant to test, without triggering the library assertion.

Something like the following should do the trick
- noexcept(std::is_nothrow_move_constructible<Tp>::value)
+ noexcept(noexcept(std::declval<Tp>() = std::declval<Tp>()))