Write the make_global_settings to the error message.

pylib/gyp/generator/make.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.
 
 # Notes:
 #
 # This is all roughly based on the Makefile system used by the Linux
 # kernel, but is a non-recursive make -- we put the entire dependency
 # graph in front of make and let it figure it out.
 #
@@ skipping 2076 matching lines @@
       needed_targets.add(target)
 
   build_files = set()
   include_list = set()
   for qualified_target in target_list:
     build_file, target, toolset = gyp.common.ParseQualifiedTarget(
         qualified_target)
 
     this_make_global_settings = data[build_file].get('make_global_settings', [])
     assert make_global_settings_array == 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))
 
     build_files.add(gyp.common.RelativePath(build_file, options.toplevel_dir))
     included_files = data[build_file]['included_files']
     for included_file in included_files:
       # The included_files entries are relative to the dir of the build file
       # that included them, so we have to undo that and then make them relative
       # to the root dir.
       relative_include_file = gyp.common.RelativePath(
           gyp.common.UnrelativePath(included_file, build_file),
           options.toplevel_dir)
@@ skipping 61 matching lines @@
     root_makefile.write("endif\n")
   root_makefile.write('\n')
 
   if (not generator_flags.get('standalone')
       and generator_flags.get('auto_regeneration', True)):
     WriteAutoRegenerationRule(params, root_makefile, makefile_name, build_files)
 
   root_makefile.write(SHARED_FOOTER)
 
   root_makefile.close()