[Bug libstdc++/69944] ctype::widen issue, use self-define do_widen, get unexpected result.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69944

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
If you define do_widen(const char*, const char*, MyChar*) correctly, you will
get the behaviour you expect.