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/glbl_ime.cpp b/src/glbl_ime.cpp
index 91d52ed..1661990 100644
--- a/src/glbl_ime.cpp
+++ b/src/glbl_ime.cpp
@@ -134,7 +134,7 @@
     if (pIApp == NULL || pIApp->OnDefWindowProc(hWnd, Msg,
 					    wParam, lParam, &lResult) != S_OK)
     {
-#if defined(WIN3264)
+#if defined(MSWIN)
 	if (wide_WindowProc)
 	    lResult = DefWindowProcW(hWnd, Msg, wParam, lParam);
 	else