Deadlock test suite

[parsonsmatt]

We should implement a test suite that runs a binary program and verifies that various configurations don't deadlock.

This needs to be managed outside of the Haskell RTS since the Haskell RTS is incapable of handling this internally. Consider:

main = do
  cancel =<< uninterruptibleMask_ $ async $ forever $ pure ()

This main loop can only be killed via a system signal, so we cannot test for the absence of a deadlock in a Haskell-only test suite. This means we'll need to have compiled binaries that the test suite builds and runs, and then verifies that they complete within some specified time.