win ninja: default to embedding manifest to match msvs

test/win/linker-flags/generate-manifest.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': 'test_generate_manifest_true',
       'type': 'executable',
       'sources': ['hello.cc'],
@@ skipping 134 matching lines @@
         },
         'VCManifestTool': {
           'EmbedManifest': 'false',
           'AdditionalManifestFiles': [
             'extra.manifest',
             'extra2.manifest',
           ],
         },
       },
     },
+    {
+      'target_name': 'test_generate_manifest_default_embed_default',
+      'type': 'executable',
+      'sources': ['hello.cc'],
+      'msvs_settings': {
+        'VCLinkerTool': {
+          'EnableUAC': 'true',
+        },
+      },
+    },
   ]
 }