[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 #22 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I'm tempted to just rip out this stuff entirely, and go back to only offering
the strong exception safety guarantee for trivially copyable types, and so
variants would only be never-valueless if all alternatives are trivially
copyable.