[Bug libstdc++/77322] [C++11] std::function::swap should be noexcept.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77322

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This has been the subject of a longstanding issue, which is only now close to
being resolved:

http://cplusplus.github.io/LWG/lwg-active.html#2062