patch 8.0.0069
Problem:    Compiler warning for self-comparison.
Solution:   Define ONE_WINDOW and add #ifdef.
diff --git a/src/buffer.c b/src/buffer.c
index 509a7bc..8b1bceb 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -4935,7 +4935,7 @@
 		    }
 #ifdef FEAT_WINDOWS
 		    /* don't close last window */
-		    if (firstwin == lastwin
+		    if (ONE_WINDOW
 			    && (first_tabpage->tp_next == NULL || !had_tab))
 #endif
 			use_firstwin = TRUE;