Fourth attempt at the following. Unreviewed, this was originally reviewed in http://codereview.c...

build/util/build_util.gyp

 # Copyright (c) 2009 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.
 
 {
   'targets': [
     {
       'target_name': 'lastchange',
       'type': 'none',
+      'toolsets': ['host', 'target'],
       'variables': {
         'lastchange_out_path': '<(SHARED_INTERMEDIATE_DIR)/build/LASTCHANGE',
         'default_lastchange_path': '../LASTCHANGE.in',
       },
       'actions': [
         {
           'action_name': 'lastchange',
           'inputs': [
             # Note:  <(default_lastchange_path) is optional,
             # so it doesn't show up in inputs.
             './lastchange.py',
           ],
           'outputs': [
             '<(lastchange_out_path).always',
             '<(lastchange_out_path)',
           ],
           'action': [
             'python', '<@(_inputs)',
             '-o', '<(lastchange_out_path)',
             '-d', '<(default_lastchange_path)',
           ],
           'message': 'Extracting last change to <(lastchange_out_path)',
           'process_outputs_as_sources': '1',
         },
       ],
     },
   ]
 }