Fix disable_nacl=1 build.

native_client_sdk/native_client_sdk_untrusted.gyp

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'includes': [
     '../build/common_untrusted.gypi',
   ],
   'conditions': [
     ['disable_nacl==0 and disable_nacl_untrusted==0', {
@@ skipping 21 matching lines @@
           },
           'sources': [
             '>!@pymod_do_main(dsc_info -s -l src/libraries/nacl_io nacl_io)',
           ],
           'dependencies': [
             '../native_client/tools.gyp:prep_toolchain',
             '../ppapi/native_client/native_client.gyp:ppapi_lib',
           ],
         },
       ],
+    }, {
+      'targets': []
     }],
   ],
 }