[Bug libstdc++/121858] function_ref(nontype_t<__fn>, _Up&& __ref) did not consider that _Up is a reference_wrapper

[hewillk at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121858

--- Comment #2 from 康桓瑋 <hewillk at gmail dot com> ---
I know it's kind of weird that rvalue reference_wrappers is not supported ​​in
this case, i.e. std::function_ref<void()> fr(std::nontype<&S::f>, std::ref(s))
is ill-formed. But that's what the current standard says.