[modules] Support star exports.

test/mjsunit/modules-imports6.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // MODULE
 
-import {b, c} from "modules-skip-2.js";
-import {a, set_a} from "modules-skip-1.js";
-import x from "modules-skip-2.js";
-
-assertEquals(42, x);
+import {b, c} from "modules-skip-4.js";
+import {a, set_a} from "modules-skip-4.js";
 
 assertEquals(1, a);
 assertEquals(1, b);
 assertEquals(1, c);
 
 set_a(2);
 assertEquals(2, a);
 assertEquals(2, b);
 assertEquals(2, c);
 
 assertThrows(() => a = 3, TypeError);
 assertThrows(() => b = 3, TypeError);
 assertThrows(() => c = 3, TypeError);
 
 assertEquals(2, a);
 assertEquals(2, b);
 assertEquals(2, c);
-
-assertThrows(() => x = 43, TypeError);
-assertEquals(42, x);