Fix attributes of length property for builtin objects (#3556)

* length property has the attributes {[[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: true} based on ECMA-262 v6, 19.2.4.1

JerryScript-DCO-1.0-Signed-off-by: HyukWoo Park hyukwoo.park@samsung.com

tests/jerry/es5.1/func-length.js

@@ -0,0 +1,19 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+var desc = Object.getOwnPropertyDescriptor(Function, "length");
+assert(desc.value === 1 &&
+        desc.writable === false &&
+        desc.enumerable === false &&
+        desc.configurable === false);