Improve generated Makefile rules for rules with 2 outputs.

test/actions-multiple-outputs/gyptest-multiple-outputs.py

+#!/usr/bin/env python
+
+# Copyright (c) 2015 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 actions with multiple outputs will correctly rebuild.
+"""
+
+import TestGyp
+import os
+
+test = TestGyp.TestGyp()
+
+test.run_gyp('multiple-outputs.gyp', chdir='src')
+
+chdir = 'relocate/src'
+test.relocate('src', chdir)
+
+def build_and_check():
+  # Build + check that both outputs exist.
+  test.build('multiple-outputs.gyp', chdir=chdir)
+  test.built_file_must_exist('out1.txt', chdir=chdir)
+  test.built_file_must_exist('out2.txt', chdir=chdir)
+
+# Plain build.
+build_and_check()
+
+# Remove either + rebuild. Both should exist (again).
+os.remove(test.built_file_path('out1.txt', chdir=chdir))
+build_and_check();
+
+# Remove the other + rebuild. Both should exist (again).
+os.remove(test.built_file_path('out2.txt', chdir=chdir))
+build_and_check();
+
+test.pass_test()