ninja: Correctly handle copies steps in sourceless shared_library targets.

test/copies/src/copies-sourceless-shared-lib.gyp

+# 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.
+
+{
+  'targets': [
+    {
+      'target_name': 'mylib',
+      'type': 'static_library',
+      'sources': [ 'foo.c' ],
+    },
+    {
+      'target_name': 'mysolib',
+      'type': 'shared_library',
+      'dependencies': [ 'mylib' ],
+      'copies': [
+        {
+          'destination': '<(PRODUCT_DIR)/copies-out',
+          'files': [ 'file1' ],
+        },
+      ],
+      # link.exe gets confused by sourceless shared libraries and needs this
+      # to become unconfused.
+      'msvs_settings': { 'VCLinkerTool': { 'TargetMachine': '1', }, },
+    },
+  ],
+}