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/GvimExt/gvimext.h b/src/GvimExt/gvimext.h
index e17f2ac..7a4e009 100644
--- a/src/GvimExt/gvimext.h
+++ b/src/GvimExt/gvimext.h
@@ -31,7 +31,7 @@
 # define STRICT
 #endif
 
-#define INC_OLE2	// WIN32, get ole2 from windows.h
+#define INC_OLE2	// MS-Windows, get ole2 from windows.h
 
 /* Visual Studio 2005 has 'deprecated' many of the standard CRT functions */
 #if defined(_MSC_VER) && _MSC_VER >= 1400