> mbcs functions don't use the wchar_t type.

That's not true. MultiByteToWideChar use LPWSTR, which is a typedef for
wchar_t*.

These functions assume that Py_UNICODE is the same type as WCHAR.

> We should just check that we are compiling under Windows:

-1, see above. In the long run, it would be really good if Python
supported a four-byte Py_UNICODE on Windows - people keep asking for it.

I have been meaning to provide versions of the mbcs codecs for years
that work for UCS-4, but haven't found the time yet to implement them.