Merge pull request #3641 from Microsoft/exportSepcifierInDeclarations

Fix assert with declaration emit for export specifier for a global

tests/cases/compiler/exportSpecifierForAGlobal.ts

@@ -0,0 +1,12 @@
+// @declaration: true
+// @module: commonjs
+
+// @filename: a.d.ts
+declare class X { }
+
+// @filename: b.ts
+export {X};
+export function f() {
+    var x: X;
+    return x;
+}