Implement missing Math functions from ES6 standard (#3593)

First step to fix issue #3568.

Changes:
- Implemented Math.clz32(), Math.fround(), Math.imul(), Math.hypot().
- Implemented all remaining Math functions with calling the standard
libm functions, but they throw UNIMPLEMENTED exception with jerry-libm,
because the necessary fdlibm functions are missing and should be ported.

All Math related test262 tests pass (except function name and length tests)

JerryScript-DCO-1.0-Signed-off-by: Csaba Osztrogonác oszi@inf.u-szeged.hu

tests/jerry/es2015/math-functions-tonumber-rule2.js

@@ -0,0 +1,23 @@
+// 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 str = "";
+var a = {valueOf: function() { str += "a"; return 1;}};
+var b = {valueOf: function() { str += "b"; return NaN;}};
+var c = {valueOf: function() { str += "c"; return 2;}};
+var d = {valueOf: function() { str += "d"; return Infinity;}};
+var e = {valueOf: function() { str += "e"; return 3;}};
+
+Math.hypot (a, b, c, d, e);
+assert (str === "abcde");