crt: replace towctype function for msvcr120.dll and UCRT

POSIX requires that `towctrans` returns its first argument unchanged when
its second argument is `(wctrans_t)0`; CRT's `towctrans` does not conform
to POSIX while mingw-w64's `towctrans` does.

This change makes POSIX-conforming `towctrans` available with all CRTs.

Signed-off-by: Kirill Makurin <maiddaisuki@outlook.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>