XCframework build script requires specific location

[freakboy3742]

The XCframework build script finds the root of the Python code checkout from the script itself through an explicit chain of .parent references. It would be more helpful if the location of the root of the checkout was found dynamically; this would allow us to symlink the location of the script in 3.14 to the location in 3.15+ so that the buildbot can work on 3.14 branches.

[freakboy3742]

Turns out I was overthinking things - the symlink reports __file__ as the original location, not the symlinked location so the existing script works fine.