The new upstream build script forces us to switch to the new python rpm
macros (PEP517/pip). There is ongoing discussion with upstream to make
builds against system libraries smoother. For now, we just patch in the
necessary libs. Note that build flags are not passed via the environment
any more.
We do not use %pyproject_buildrequires because it only finds
pip/setuptools and trips over wrong pyproject.toml entries.
