patch 8.0.1792: MS-Windows users expect -? to work like --help

Problem:    MS-Windows users expect -? to work like --help.
Solution:   Add -?. (Christian Brabandt, closes #2867)
diff --git a/src/main.c b/src/main.c
index 3b366b5..e2686b8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2014,6 +2014,7 @@
 #endif
 		break;
 
+	    case '?':		/* "-?" give help message (for MS-Windows) */
 	    case 'h':		/* "-h" give help message */
 #ifdef FEAT_GUI_GNOME
 		/* Tell usage() to exit for "gvim". */