CI status

Hi everyone, As you likely have noticed, GHC's CI is a bit of a mess since the Hadrian merge, especially for differentials based on commits prior to the merge. The problem is a tiresome limitation of Harbormaster's CI strategy [1]. I have taken this opportunity to finally move testing of Differentials to CircleCI. Unfortunately this has taken longer than anticipated due to more tiresome Phabricator issues. At the moment the only guidance I can offer for those in need of CI is to sit tight; the problem is being worked on. Cheers, - Ben [1] Namely, Harbormaster attempts to reuse working trees to perform builds. However, it fails to remove stale submodules, meaning any attempt to checkout a post-Hadrian-merge commit fails.