Write the make_global_settings to the error message.

pylib/gyp/generator/ninja.py

 # Copyright (c) 2013 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.
 
 import copy
 import hashlib
 import json
 import multiprocessing
 import os.path
 import re
@@ skipping 2009 matching lines @@
   # objects.
   target_short_names = {}
 
   for qualified_target in target_list:
     # qualified_target is like: third_party/icu/icu.gyp:icui18n#target
     build_file, name, toolset = \
         gyp.common.ParseQualifiedTarget(qualified_target)
 
     this_make_global_settings = data[build_file].get('make_global_settings', [])
     assert make_global_settings == this_make_global_settings, (
-        "make_global_settings needs to be the same for all targets.")
+        "make_global_settings needs to be the same for all targets. %s vs. %s" %
+        (this_make_global_settings, make_global_settings))
 
     spec = target_dicts[qualified_target]
     if flavor == 'mac':
       gyp.xcode_emulation.MergeGlobalXcodeSettingsToSpec(data[build_file], spec)
 
     build_file = gyp.common.RelativePath(build_file, options.toplevel_dir)
 
     base_path = os.path.dirname(build_file)
     obj = 'obj'
     if toolset != 'target':
@@ skipping 82 matching lines @@
           arglists.append(
               (target_list, target_dicts, data, params, config_name))
         pool.map(CallGenerateOutputForConfig, arglists)
       except KeyboardInterrupt, e:
         pool.terminate()
         raise e
     else:
       for config_name in config_names:
         GenerateOutputForConfig(target_list, target_dicts, data, params,
                                 config_name)