Surprisingly hard to get the build to work.  I feel like no one must use
libTooling for out-of-tree projects.  Also, the binary can only be run from
the directory in which it would have been placed for an in-tree project.

It was going to be a refcount discipline checker, but I'm not sure that's
a good use of time right now.  I want to check it in though so that we have it.