[Bug libstdc++/60695] std::atomic<X> doesn't work when X is of zero size

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60695

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I don't buy it. That zero-size struct type has very limited uses, it's not the
sort of type you use like other value types, and I can't imagine any scenario
where that type is useful where you're also storing generic types in
std::atomic.

I don't want to complicate the implementation even if someone thinks of an
obscure hypothetical use case.