This completes the out of tree build CLI. This PR is paired up with:
numpy/numpy#21895
I have also successfully built scikit-learn, statsmodels, pandas, and
astropy with this.
The last thing we need to do after this is set up deployment of the
cross build environment. We can deploy one version to s3 for each
tagged commit. I will do that in a separate PR after this is merged.
Hood Chatham