symbol.c: suppress warnings

* symbol.c (rb_id_serial_to_id): suppress unused-function warnings
  where ID_TABLE_IMPL is 0, 1, or 11.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51684 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

symbol.c

@@ -400,6 +400,9 @@ get_id_entry(rb_id_serial_t num, const enum id_entry_type t)
 }
 
 static inline ID
+#ifdef __GNUC__
+__attribute__((unused))
+#endif
 rb_id_serial_to_id(rb_id_serial_t num)
 {
     if (is_notop_id((ID)num)) {