Don't try to use -MMD / .o.d depfiles for ninja with .s files.

test/ninja/s-needs-no-depfiles/gyptest-s-needs-no-depfiles.py

+#!/usr/bin/env python
+
+# Copyright (c) 2012 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.
+
+"""
+Verify that .s files don't always trigger a rebuild, as would happen if depfiles
+were used for them (since clang & gcc ignore -MMD when building .s->.o on
+linux).
+"""
+
+import os
+import sys
+import TestCommon
+import TestGyp
+
+# NOTE(fischman): Each generator uses depfiles (or not) differently, so this is
+# a ninja-specific test.
+test = TestGyp.TestGyp(formats=['ninja'])
+
+if sys.platform == 'win32' or sys.platform == 'win64':
+  # This test is about clang/gcc vs. depfiles; VS gets a pass.
+  test.pass_test()
+  sys.exit(0)
+
+test.run_gyp('s-needs-no-depfiles.gyp')
+
+# Build the library, grab its timestamp, rebuild the library, ensure timestamp
+# hasn't changed.
+test.build('s-needs-no-depfiles.gyp', 'empty')
+empty_dll = test.built_file_path('empty', test.SHARED_LIB)
+test.built_file_must_exist(empty_dll)
+pre_stat = os.stat(test.built_file_path(empty_dll))
+test.sleep()
+test.build('s-needs-no-depfiles.gyp', 'empty')
+post_stat = os.stat(test.built_file_path(empty_dll))
+
+if pre_stat.st_mtime != post_stat.st_mtime:
+  test.fail_test()
+else:
+  test.pass_test()