Add the fallthrough attribute to notify gcc7 that it's on purpose.

Signed-off-by: Gary Lin <glin@suse.com>
Signed-off-by: Nigel Croxon <ncroxon@redhat.com>

lib/print.c

@@ -1131,6 +1131,9 @@ Returns:
             case 'X':
                 Item.Width = Item.Long ? 16 : 8;
                 Item.Pad = '0';
+#if __GNUC__ >= 7
+		__attribute__ ((fallthrough));
+#endif
             case 'x':
                 ValueToHex (
                     Item.Scratch,