[Bug libstdc++/60710] experimental::optional is using T::operator!=

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60710

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The current Fundamentals TS draft (n3848) doesn't have those operator!=
overloads at all, so we may want to remove them entirely rather than fix them
... I'm not sure yet.