Introduce a BuiltinsConstructStub that sets up new.target and does a [[call]] per ES6 9.3.2

src/execution.cc

Index: src/execution.cc
diff --git a/src/execution.cc b/src/execution.cc
index cc067a8ab88ca61ca95878f68d96eb49fd5f815d..a209bc35fae48346f1df7db888cc0db451437dcc 100644
--- a/src/execution.cc
+++ b/src/execution.cc
@@ -457,20 +457,6 @@ MaybeHandle<Object> Execution::ToObject(Isolate* isolate, Handle<Object> obj) {
 }
 
 
-MaybeHandle<JSRegExp> Execution::NewJSRegExp(Handle<String> pattern,
-                                             Handle<String> flags) {
-  Isolate* isolate = pattern->GetIsolate();
-  Handle<JSFunction> function = Handle<JSFunction>(
-      isolate->native_context()->regexp_function());
-  Handle<Object> re_obj;
-  ASSIGN_RETURN_ON_EXCEPTION(
-      isolate, re_obj,
-      RegExpImpl::CreateRegExpLiteral(function, pattern, flags),
-      JSRegExp);
-  return Handle<JSRegExp>::cast(re_obj);
-}
-
-
 Handle<String> Execution::GetStackTraceLine(Handle<Object> recv,
                                             Handle<JSFunction> fun,
                                             Handle<Object> pos,