message: Fix a distracting error message on Linux
diff: @@ -84,12 +84,13 @@ swift_sdk_root = None
  def getSwiftSDKRoot():
  """Returns the SDK root to be used for compiling Swift/ObjC interop code."""
  global swift_sdk_root
  + import platform
  if swift_sdk_root is None:
  if "SDKROOT" in os.environ:
  swift_sdk_root = os.environ["SDKROOT"]
  if "SWIFTSDKROOT" in os.environ:
  swift_sdk_root = os.environ["SWIFTSDKROOT"]
  - else:
  + elif platform.system() == 'Darwin':
  try:
  sdk_path = subprocess.check_output(
  'xcrun -sdk macosx --show-sdk-path', shell=True)
  