[Bug c++/67777] unsigned wchar_t and signed wchar_t should cause compiler errors but do not.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67777

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Trevor Hickey from comment #0)
> Why can we add signed/unsigned qualifiers to wchar_t?  

It produces a type of the same size but with the opposite signedness, like
std::make_signed/std::make_unsigned.