Set --max-jobs when running in CI
This removes the hard coding of max-jobs
which allows ninja builds to run unbounded on your laptop.
Instead we set --max-jobs
to $(( $(nproc) / 4 ))
on the bst
command line (one quarter of the available cores on the host we're building on, since we still use the default number of 4 maximum parallel builds).
This fixes #165 (closed)