Set ZERO_AR_DATE=1 when running libtool.

test/mac/gyptest-libtool-zero.py

Index: test/mac/gyptest-libtool-zero.py
===================================================================
--- test/mac/gyptest-libtool-zero.py	(working copy)
+++ test/mac/gyptest-libtool-zero.py	(working copy)
@@ -1,11 +1,11 @@
 #!/usr/bin/env python
 
-# Copyright (c) 2012 Google Inc. All rights reserved.
+# Copyright (c) 2014 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.
 
 """
-Verifies that compile-time flags work.
+Verifies libraries have proper mtime.
 """
 
 import TestGyp
@@ -14,7 +14,13 @@
 
 if sys.platform == 'darwin':
   test = TestGyp.TestGyp(formats=['ninja', 'make', 'xcode'])
-  CHDIR = 'cflags'
+
+  CHDIR = 'libtool-zero'
+
   test.run_gyp('test.gyp', chdir=CHDIR)
-  test.build('test.gyp', test.ALL, chdir=CHDIR)
+
+  test.build('test.gyp', 'mylib', chdir=CHDIR)
+
+  test.up_to_date('test.gyp', 'mylib', chdir=CHDIR)
+
   test.pass_test()