3.9 hangs on compileall with -j 12
@mgorny reports that the following hangs occasionally:
/tmp/portage/dev-python/pypy3-7.3.8_rc1/image/usr/bin/pypy3-c-7.3.8_rc1 -O -m compileall -j 12 -q -f -d /usr/lib/pypy3.9 /tmp/portage/dev-python/pypy3-7.3.8_rc1/image/usr/lib/pypy3.9