Add builtin detector to generate-runtime-tests.py

src/v8natives.js

Index: src/v8natives.js
diff --git a/src/v8natives.js b/src/v8natives.js
index 46dfab41b86c286a1661c26142cb45a91edf2355..80b1f9af7721a9d43d35a249ec60b30f45324028 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -1886,6 +1886,9 @@ function RunMicrotasksJS() {
 }
 
 function EnqueueMicrotask(fn) {
+  if (!IS_FUNCTION(func)) {
+    throw new $TypeError('Can only enqueue functions');
+  }
   var microtaskState = %GetMicrotaskState();
   if (IS_UNDEFINED(microtaskState.queue) || IS_NULL(microtaskState.queue)) {
     microtaskState.queue = new InternalArray;