def _GetHost(cpu, target_os):
  """Returns the host triple for the given OS and CPU."""
  if cpu == 'x64':
    cpu = 'x86_64'
  elif cpu == 'arm64':
    cpu = 'aarch64'

  if target_os == 'linux':
    return cpu + '-unknown-linux'
  elif target_os == 'mac':
    return cpu + '-apple-darwin'
  elif target_os == 'ios':
    return cpu + '-ios-darwin'
  else:
    raise RuntimeError('Unsupported host')