What I don't quite understand is why the build fails for you but passes for me. What configure flags did you use?

This version should fare better:

def is_macosx_sdk_path(path):
    """
    Returns True if 'path' can be located in an OSX SDK
    """
    return (path.startswith('/usr/') and not path.startswith('/usr/local')) or path.startswith('/System/')

This explicitly tests for paths that must be in the SDK:

* Anything in /System is owned by the system, and should be fetched
  through the SDK
* Likewise for anything in /usr that isn't in /usr/local
 
IMHO anyone that installs additional libraries in /usr/lib, or /System/Libraries/Frameworks is confused at best, and we shouldn't even try to support that.


The repository contains an simpler (but in hindsight too simple) version because ${SDKROOT}/usr/local/lib is a symlink to the real /usr/local/lib. That works fine when looking for libraries, but not when looking for other files (such as headers).