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/getchar.c b/src/getchar.c
index eaef1ab..7039c9c 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -1623,7 +1623,7 @@
 	    }
 	    c = TO_SPECIAL(c2, c);
 
-#if defined(FEAT_GUI_W32) && defined(FEAT_MENU) && defined(FEAT_TEAROFF)
+#if defined(FEAT_GUI_MSWIN) && defined(FEAT_MENU) && defined(FEAT_TEAROFF)
 	    /* Handle K_TEAROFF here, the caller of vgetc() doesn't need to
 	     * know that a menu was torn off */
 	    if (c == K_TEAROFF)
@@ -1679,7 +1679,7 @@
 	    case K_KMULTIPLY:	c = '*'; break;
 	    case K_KENTER:	c = CAR; break;
 	    case K_KPOINT:
-#ifdef WIN32
+#ifdef MSWIN
 				// Can be either '.' or a ',',
 				// depending on the type of keypad.
 				c = MapVirtualKey(VK_DECIMAL, 2); break;
@@ -3107,7 +3107,7 @@
 	if (p[0] == NUL || (p[0] == K_SPECIAL
 		    /* timeout may generate K_CURSORHOLD */
 		    && (i < 2 || p[1] != KS_EXTRA || p[2] != (int)KE_CURSORHOLD)
-#if defined(WIN3264) && !defined(FEAT_GUI)
+#if defined(MSWIN) && !defined(FEAT_GUI)
 		    /* Win32 console passes modifiers */
 		    && (i < 2 || p[1] != KS_MODIFIER)
 #endif