patch 8.1.1557: compiler warning for unused variables in tiny version

Problem:    Compiler warning for unused variables in tiny version. (Tony
            Mechelynck)
Solution:   Add #ifdef.
diff --git a/src/version.c b/src/version.c
index 4eb37a7..f6bb71c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1557,
+/**/
     1556,
 /**/
     1555,