Use cibuildwheel in the build

We should look at cibuildwheel and possibly removing the complicated scripting subrepos. We actually use very little of multibuild, mainly to build in dockers for linux. Instead, cibuildwheel could do this for us. We also use gfortran compilers from gfortran_install on macos, but the subrepo carries an unused achives directory. We could vendor the single gfortran_utils.sh script file instead.