Allow mojo_debug to run on mac

mojo/devtools/common/mojo_debug

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 import argparse
 import codecs
 import logging
 import os.path
+import platform
 import requests
 import signal
 import subprocess
 import sys
 import tempfile
 
 
 from android_gdb.install_remote_file_reader import install
 from devtoolslib import paths
 
@@ skipping 167 matching lines @@
       return
     else:
       raise
 
   gdb_path = os.path.join(
       ndk_dir,
       'toolchains',
       # TODO(etiennej): Always select the most recent toolchain?
       'arm-linux-androideabi-4.9',
       'prebuilt',
-      # TODO(etiennej): DEPS mac NDK and use it on macs.
-      'linux-x86_64',
+      '%s-%s' % (platform.system().lower(), platform.machine()),
       'bin',
       'arm-linux-androideabi-gdb')
   python_gdb_script_path = os.path.join(os.path.dirname(__file__),
                                         'android_gdb', 'session.py')
   debug_session_arguments = {}
   if args.build_dir:
     debug_session_arguments["build_directory_list"] = ','.join(args.build_dir)
   else:
     try:
       debug_session_arguments["build_directory_list"] = os.path.join(
@@ skipping 95 matching lines @@
   subparsers = parser.add_subparsers(help='the tool to run')
   _add_device_command(subparsers)
   _add_tracing_command(subparsers)
   _add_gdb_command(subparsers)
 
   args = parser.parse_args()
   return args.func(args)
 
 if __name__ == '__main__':
   sys.exit(main())