[BUG] No greeting is printed when compiled with mingw-w64

[Matthew Palermo]

Hi all,

I think there is a problem with GNU hello 2.10 when compiled with
mingw-w64 on Windows. GNU hello will not output any greeting, only a
newline.

Specifically, I think the problem is one with the mingw-w64-crt
implementation of mbsrtowcs. GNU hello assumes, I think correctly,
that the first invocation of mbsrtowcs doesn't change the greeting_msg
pointer position. But as seen in the source code of mingw-w64-crt
(https://github.com/Alexpux/mingw-w64/blob/master/mingw-w64-crt/misc/mbrtowc.c),
this isn't implemented and the pointer is moved to the end of the
string as normal. The result is an empty greeting_msg string passed to
the second mbsrtowcs invocation.

Clearly the proper solution (If I'm right about this) is to fix the
problem in mingw-w64-crt. I just wanted to submit this as a learning
process, hopefully get some feedback and just chat. I'm not very
practiced in C development, only just enough to do minor debugging and
hacking.

Regards,
Matthew