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

[dawid_jurek at vp dot pl]

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

--- Comment #1 from dawid_jurek at vp dot pl ---
Created attachment 39471
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39471&action=edit
Fix bug in operator=