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/globals.h b/src/globals.h
index 82e663e..729a269 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -19,7 +19,7 @@
  */
 EXTERN long	Rows			/* nr of rows in the screen */
 #ifdef DO_INIT
-# if defined(WIN3264)
+# if defined(MSWIN)
 			    = 25L
 # else
 			    = 24L
@@ -818,7 +818,7 @@
 EXTERN int	enc_unicode INIT(= 0);	/* 2: UCS-2 or UTF-16, 4: UCS-4 */
 EXTERN int	enc_utf8 INIT(= FALSE);		/* UTF-8 encoded Unicode */
 EXTERN int	enc_latin1like INIT(= TRUE);	/* 'encoding' is latin1 comp. */
-#if defined(WIN3264) || defined(FEAT_CYGWIN_WIN32_CLIPBOARD)
+#if defined(MSWIN) || defined(FEAT_CYGWIN_WIN32_CLIPBOARD)
 /* Codepage nr of 'encoding'.  Negative means it's not been set yet, zero
  * means 'encoding' is not a valid codepage. */
 EXTERN int	enc_codepage INIT(= -1);
@@ -826,7 +826,7 @@
 #endif
 EXTERN int	has_mbyte INIT(= 0);		/* any multi-byte encoding */
 
-#if defined(WIN3264)
+#if defined(MSWIN)
 EXTERN int	wide_WindowProc INIT(= FALSE);	/* use wide WindowProc() */
 #endif
 
@@ -1296,7 +1296,7 @@
 EXTERN int	echo_wid_arg INIT(= FALSE);	/* --echo-wid argument */
 #endif
 
-#ifdef FEAT_GUI_W32
+#ifdef FEAT_GUI_MSWIN
 /*
  * The value of the --windowid argument.
  * For embedding gvim inside another application.
@@ -1645,7 +1645,7 @@
 EXTERN int *eval_lavars_used INIT(= NULL);
 #endif
 
-#ifdef WIN3264
+#ifdef MSWIN
 EXTERN int ctrl_break_was_pressed INIT(= FALSE);
 #endif