Resurrect yjit_hook

Author: k0kubun

ruby.c

@@ -1823,9 +1823,11 @@ ruby_opt_init(ruby_cmdline_options_t *opt)
     }
 #endif
 
+#if USE_YJIT
     // Call yjit_hook.rb after rb_yjit_init() to use `RubyVM::YJIT.enabled?`
-    //void Init_builtin_yjit_hook();
-    //Init_builtin_yjit_hook();
+    void Init_builtin_yjit_hook();
+    Init_builtin_yjit_hook();
+#endif
 
     ruby_set_script_name(opt->script_name);
     require_libraries(&opt->req_list);