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

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index c0d7a20069118dafacccf1a08513f7faee4d03eb..cc1601a9b1a9fe8a8928b9530fe4ae9dec3631f5 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -222,6 +222,7 @@ enum BindingFlags {
   V(OBJECT_FUNCTION_INDEX, JSFunction, object_function)                        \
   V(OBJECT_FUNCTION_PROTOTYPE_MAP_INDEX, Map, object_function_prototype_map)   \
   V(OPAQUE_REFERENCE_FUNCTION_INDEX, JSFunction, opaque_reference_function)    \
+  V(PROXY_FUNCTION_INDEX, JSFunction, proxy_function)                          \
   V(REGEXP_FUNCTION_INDEX, JSFunction, regexp_function)                        \
   V(REGEXP_RESULT_MAP_INDEX, Map, regexp_result_map)                           \
   V(RUNTIME_CONTEXT_INDEX, Context, runtime_context)                           \