patch 8.1.0941: macros for MS-Windows are inconsistent

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 #3932)
diff --git a/src/message.c b/src/message.c
index ed59d1b..621edb9 100644
--- a/src/message.c
+++ b/src/message.c
@@ -2556,7 +2556,7 @@
 msg_use_printf(void)
 {
     return (!msg_check_screen()
-#if defined(WIN3264) && !defined(FEAT_GUI_MSWIN)
+#if defined(MSWIN) && !defined(FEAT_GUI_MSWIN)
 	    || !termcap_active
 #endif
 	    || (swapping_screen() && !termcap_active)
@@ -2573,7 +2573,7 @@
     char_u	*buf = NULL;
     char_u	*p = s;
 
-#ifdef WIN3264
+#ifdef MSWIN
     if (!(silent_mode && p_verbose == 0))
 	mch_settmode(TMODE_COOK);	/* handle CR and NL correctly */
 #endif
@@ -2633,7 +2633,7 @@
 
     msg_didout = TRUE;	    // assume that line is not empty
 
-#ifdef WIN3264
+#ifdef MSWIN
     if (!(silent_mode && p_verbose == 0))
 	mch_settmode(TMODE_RAW);
 #endif
@@ -2934,7 +2934,7 @@
     void
 mch_errmsg(char *str)
 {
-#if defined(WIN3264) && !defined(FEAT_GUI_MSWIN)
+#if defined(MSWIN) && !defined(FEAT_GUI_MSWIN)
     int	    len = (int)STRLEN(str);
     DWORD   nwrite = 0;
     DWORD   mode = 0;
@@ -3022,7 +3022,7 @@
     void
 mch_msg(char *str)
 {
-#if defined(WIN3264) && !defined(FEAT_GUI_MSWIN)
+#if defined(MSWIN) && !defined(FEAT_GUI_MSWIN)
     int	    len = (int)STRLEN(str);
     DWORD   nwrite = 0;
     DWORD   mode;
@@ -4008,7 +4008,7 @@
 	    filter = BROWSE_FILTER_DEFAULT;
 	if (flags & BROWSE_DIR)
 	{
-#  if defined(FEAT_GUI_GTK) || defined(WIN3264)
+#  if defined(FEAT_GUI_GTK) || defined(MSWIN)
 	    /* For systems that have a directory dialog. */
 	    fname = gui_mch_browsedir(title, initdir);
 #  else
@@ -4754,7 +4754,7 @@
 			else if (length_modifier == 'L')
 			{
 # ifdef FEAT_NUM64
-#  ifdef WIN3264
+#  ifdef MSWIN
 			    f[f_l++] = 'I';
 			    f[f_l++] = '6';
 			    f[f_l++] = '4';