`make devenv` errors

[iaindillingham]

make devenv errors:

venv/bin/pip-compile setup.py --extra drivers -o requirements.prod.txt
Backend subprocess exited when trying to invoke get_requires_for_build_wheel
Failed to parse /Users/iaindillingham/Code/opensafely-core/cohort-extractor/setup.py
make: *** [Makefile:25: requirements.prod.txt] Error 2

pip install . into a new virtual env is more informative:

Version 'not-from-a-package' is not valid according to PEP 440.