python setup.py clean --all does not remove ffi/build

[ARF1]

If one calls python setup.py build the directory ffi/build is created. python setup.py clean --all does not remove it however.

This is a problem because stale builds can persist. For example pip install . fails because of this if python setup.py build was previously executed.

[esc]

@ARF1 thanks for submitting this. Can you discern, if this caused by the code Numba developers wrote in the setup.py or is this a failure of the Python build system?

[ARF1]

@esc I have never really written a non-trivial setup.py but I think setup.py is to blame. - At least indirectly: From what I can tell at a glance ffi/build is created by ffi/build.py - which is somehow called by setup.py. But unless setup.py is told about the directory created by ffi/build.py it has no way to know about it. - That is just my guess though. I have not really looked into it.

[seibert]

@sklam wrote this originally, and it was doing some hacky things to try to handle building a standalone shared library that isn't a Python extension. Not sure if he recalls how this was supposed to work.

[ARF1]

Fix in #569