Because these processes are expected to crash, generating a core dump
from them and throwing up a CrashReporter window is less helpful than
it is distracting while running many tests at a time.
Use the prctl for controlling the core dump-able flag to tell the kernel
we don't want core dumps from these processes. Note that because we also
build LibTest for Lagom, we have to check for MacOS which doesn't
support prctl(PR_SET_DUMPABLE).
