[Bug libstdc++/87431] valueless_by_exception() should unconditionally return false if all the constructors are noexcept

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87431

--- Comment #18 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Proposed new patch posted:
https://gcc.gnu.org/ml/gcc-patches/2019-04/msg00142.html