This is a greatly simplified Docker container compared to that in
compiler/. We really want the docker image to just be a build
environment, and build the specific versions of dependencies as part of
our normal build (not docker build).
It also includes a helper script that lets you easily do build actions
with the docker environment, but into a checkout on the host. This can
dramatically reduce the pain in building from the docker container as
the source doesn't need to be checked out and only caches are lost
between invocations.
Eric Anderson