Support Mac android cross compile.

pylib/gyp/__init__.py

Index: pylib/gyp/__init__.py
===================================================================
--- pylib/gyp/__init__.py	(revision 1452)
+++ pylib/gyp/__init__.py	(working copy)
@@ -298,6 +298,9 @@
   parser.add_option('--toplevel-dir', dest='toplevel_dir', action='store',
                     default=None, metavar='DIR', type='path',
                     help='directory to use as the root of the source tree')
+  parser.add_option('--host-flavor', dest='host_flavor', action='store',
+                    env_name='GYP_HOST_FLAVOR', regenerate=False,
+                    help='To override the value of the build os')

[Torne, 2012/08/14 11:04:01]

Help messages don't start with a capital, and "to" is redundant. How about
"overrides host OS flavor used to crosscompile" ?

   # --no-circular-check disables the check for circular relationships between
   # .gyp files.  These relationships should not exist, but they've only been
   # observed to be harmful with the Xcode generator.  Chromium's .gyp files
@@ -329,6 +332,9 @@
   options, build_files_arg = parser.parse_args(args)
   build_files = build_files_arg
 
+  if not options.host_flavor:

[Torne, 2012/08/14 11:04:01]

needs to also be "and options.use_environment"

+    options.host_flavor = os.environ.get('GYP_HOST_FLAVOR', '')
+
   if not options.formats:
     # If no format was given on the command line, then check the env variable.
     generate_formats = []