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

test/same-rule-output-file-name/src/subdir2/subdir2.gyp

+# 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.
+
+{
+  'targets': [
+    {
+      'target_name': 'target2',
+      'type': 'none',
+      'sources': [
+        '../touch.py'
+      ],
+      'rules': [
+        {
+          'rule_name': 'rule2',
+          'extension': 'py',
+          'inputs': [],
+          'outputs': [
+            'rule.txt',
+          ],
+          'action': [
+            'python', '../touch.py', '<(_outputs)',
+          ],
+          # Allows the test to run without hermetic cygwin on windows.
+          'msvs_cygwin_shell': 0,
+        },
+      ],
+    },
+  ],
+}