Make sure that export * from does not overwrite named exports.

packages/babel-plugin-transform-es2015-modules-commonjs/test/fixtures/strict/export-all/expected.js

@@ -3,6 +3,15 @@
 Object.defineProperty(exports, "__esModule", {
   value: true
 });
+var _exportNames = {
+  z: true,
+  a: true,
+  b: true,
+  d: true,
+  e: true,
+  f: true,
+  c: true
+};
 exports.b = b;
 exports.default = _default;
 Object.defineProperty(exports, "c", {
@@ -17,6 +26,7 @@ var _mod = require("mod");
 
 Object.keys(_mod).forEach(function (key) {
   if (key === "default" || key === "__esModule") return;
+  if (Object.prototype.hasOwnProperty.call(_exportNames, key)) return;
   Object.defineProperty(exports, key, {
     enumerable: true,
     get: function () {