Adds generator support for Xcode 5 xctest targets.

test/mac/xctest/TestCase.m

Index: test/mac/xctest/TestCase.m
===================================================================
--- test/mac/xctest/TestCase.m	(revision 0)
+++ test/mac/xctest/TestCase.m	(working copy)
@@ -0,0 +1,16 @@
+// Copyright (c) 2013 Google Inc. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <XCTest/XCTest.h>
+#import "MyClass.h"
+
+@interface TestCase : XCTestCase
+@end
+
+@implementation TestCase
+- (void)testFoo {
+  MyClass *foo = [[MyClass alloc] init];
+  XCTAssertNotNil(foo, @"expected non-nil object");
+}
+@end