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This also solves a difficulty with the Cython import in setuptools' build_ext. We need to inherit from the one in distutils, so that setuptools can inherit from us. That leads to a circular dependency that goes either way depending on which gets imported first by users, and in what way (from-import or module import). This is built to match the code in

https://github.com/pypa/setuptools/blob/9f1822ee910df3df930a98ab99f66d18bb70659b/setuptools/command/build_ext.py#L14-L21

Closes https://github.com/cython/cython/issues/3541