patch 8.1.2284: compiler warning for unused variable

Problem:    Compiler warning for unused variable. (Tony Mechelynck)
Solution:   Add #ifdef.
diff --git a/src/version.c b/src/version.c
index d8eedea..64efb6e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2284,
+/**/
     2283,
 /**/
     2282,