It looks like Chisel fails when I try to run it in parallel. This adds a lock
file to ensure that only a single Chisel instance is running at a time when
running the regressions.
In order to have the buildbot support various types of failures it needs
to run different commands. Rather than modifying the regression script
to have a bunch of arguments I've just gone and made a makefile for
regressions instead.
This doesn't run torture right now because that's broken, but I'll add
support soon.