patch 8.0.0192: cannot build with tiny features

Problem:    Build fails with tiny features.
Solution:   Change #ifdef for hash_clear().  Avoid warning for unused
            argument.
diff --git a/src/if_cscope.c b/src/if_cscope.c
index 31c0371..60480a5 100644
--- a/src/if_cscope.c
+++ b/src/if_cscope.c
@@ -207,7 +207,7 @@
     static void
 do_cscope_general(
     exarg_T	*eap,
-    int		make_split) /* whether to split window */
+    int		make_split UNUSED) /* whether to split window */
 {
     cscmd_T *cmdp;