Merge pull request #5370 from weswigham/system-export-var

Fix system export var when targeting ES6

src/compiler/emitter.ts

@@ -2770,7 +2770,7 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, Promi
              *   we we emit variable statement 'var' should be dropped.
              */
             function isSourceFileLevelDeclarationInSystemJsModule(node: Node, isExported: boolean): boolean {
-                if (!node || languageVersion >= ScriptTarget.ES6 || !isCurrentFileSystemExternalModule()) {
+                if (!node || !isCurrentFileSystemExternalModule()) {
                     return false;
                 }
 

tests/baselines/reference/systemModule1.js

@@ -8,7 +8,7 @@ System.register([], function(exports_1) {
     return {
         setters:[],
         execute: function() {
-            x = 1;
+            exports_1("x", x = 1);
         }
     }
 });