patch 9.0.0689: compiler warning for unused function

Problem:    Compiler warning for unused function.
Solution:   Add #ifdef. (John Marriott)
diff --git a/src/version.c b/src/version.c
index 2108099..1d60238 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    689,
+/**/
     688,
 /**/
     687,