[Bug c++/120460] std::function ignores [[nodiscard]] attribute

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120460

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
i.e. maybe this warning should ignore whether it's in a system header or not.