Fix issue with absolute path with Python 3.13 on Windows

[adang1345]

Fix #4669

Summary of changes

Fix an issue with Python 3.13 on Windows where specifying the absolute path to an extension module source file would cause the build files to be written to the directory containing the source file.

Closes #4669

Pull Request Checklist

• Changes have tests
• News fragment added in newsfragments/.
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I tested this change manually by using the setup.py and simpleext.c files in the bug report and executing py -3.13 setup.py build_ext. Before this change, the build files were written to the directory containing these files. After this change, the build files were instead written to build/temp.win-amd64-cpython-313. I am not sure whether there is an easy way to add an automated test for this.

[abravalheri]

Hi @adang1345 thank you very much for working on this.

The problem is likely related to a change in Python 3.13: https://docs.python.org/3.13/whatsnew/3.13.html#os-path.

Could you please contribute the change directly to https://github.com/pypa/distutils?

Everything under the setuptools/_distutils folder is merged directly from https://github.com/pypa/distutils and we cannot change it directly in setuptools (otherwise it would be overwritten next time we bring updates from pypa/distutils).

[adang1345]

I opened a pull request at pypa/distutils#302.