Python 2.7's setup.py has incorrect behaviour when adding the SDKROOT to the beginning of the include path while searching.

When searching paths, find_file first checks is_macosx_sdk_path  to see if it needs to add the sdk_root: https://github.com/python/cpython/blob/2.7/setup.py#L87-L88

This is mostly correct, except one of the path prefixes it checks is /Library: https://github.com/python/cpython/blob/2.7/setup.py#L64

The Xcode CLT path is located in /Library, so this check passes. That means the /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk portion of the path gets repeated, leading to an invalid path.

I recognize Python 2.7 isn't in active development, but I have a minimal patch to fix this that I will be submitting.