Fix make backend to correctly handle rules with output files of the same name

test/same-rule-output-file-name/gyptest-all.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.
+
+"""
+Tests the use of rules with the same output file name.
+"""
+
+import TestGyp
+
+test = TestGyp.TestGyp()
+
+test.run_gyp('subdirs.gyp', chdir='src')
+
+test.relocate('src', 'relocate/src')
+
+test.build('subdirs.gyp', test.ALL, chdir='relocate/src')
+test.must_exist('relocate/src/subdir1/rule.txt')
+test.must_exist('relocate/src/subdir2/rule.txt')
+
+test.pass_test()