patch 8.0.0069
Problem:    Compiler warning for self-comparison.
Solution:   Define ONE_WINDOW and add #ifdef.
diff --git a/src/quickfix.c b/src/quickfix.c
index c3def1b..a45faea 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -2137,7 +2137,7 @@
 	 * If there is only one window and it is the quickfix window, create a
 	 * new one above the quickfix window.
 	 */
-	if (((firstwin == lastwin) && bt_quickfix(curbuf)) || !usable_win)
+	if ((ONE_WINDOW && bt_quickfix(curbuf)) || !usable_win)
 	{
 	    flags = WSP_ABOVE;
 	    if (ll_ref != NULL)