patch 8.1.2160: cannot build with +syntax but without +terminal

Problem:    Cannot build with +syntax but without +terminal.
Solution:   Add #ifdef.
diff --git a/src/version.c b/src/version.c
index 91cffb3..9135fe7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2160,
+/**/
     2159,
 /**/
     2158,