Building OpenBLAS

This is a repository to trigger builds of OpenBLAS on Travis-CI (for aarch64, ppc64, s390x) and github actions for all the others.

The OpenBLAS libraries get uploaded to https://anaconda.org/multibuild-wheels-staging/openblas-libs/files

A project using these libraries, for Manylinux or macOS, will need the gfortran-install submodule used here, from https://github.com/MacPython/gfortran-install