[Bug libstdc++/77288] Std::experimental::optional::operator= implementation is broken in gcc 6.1

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77288

--- Comment #5 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Ah. That would indeed mean that every converting assignment introduces
a temporary. Design-wise I'd rather have it so that optional doesn't convert
at all in the assignment. :)