Docker restricts the number of processes in a container to some
limit it calculates. This limit turns out to be too low on large
machines, since we run multiple links in parallel, and each link
runs many threads.
Remove the limit by specifying --pids-limit -1. Since dbuild is
meant to provide a build environment, not a security barrier,
this is okay (the container is still restricted by host limits).
I checked that --pids-limit is supported by old versions of
docker and by podman.
Fixes#5651.
Message-Id: <20200127090807.3528561-1-avi@scylladb.com>