vim-patch:8.1.0941: macros for MS-Windows are inconsistent (#20215)

Problem:    Macros for MS-Windows are inconsistent, using "32", "3264 and
            others.
Solution:   Use MSWIN for all MS-Windows builds.  Use FEAT_GUI_MSWIN for the
            GUI build. (Hirohito Higashi, closes vim/vim#3932)
4f97475d32

src/nvim/buffer.c

@@ -3448,7 +3448,7 @@ void fname_expand(buf_T *buf, char **ffname, char **sfname)
   }
   *ffname = fix_fname((*ffname));     // expand to full path
 
-#ifdef WIN32
+#ifdef MSWIN
   if (!buf->b_p_bin) {
     // If the file name is a shortcut file, use the file it links to.
     char *rfname = os_resolve_shortcut((const char *)(*ffname));