In master, we build against the latest build out of that repo, which comes from the libffi branch (not the 3.3.0 RC).

In 3.8 (and 3.7? I forget) we use the 3.3.0 RC build. There's no later release from libffi (last I checked), and no important fixes since then (only ARM64 support, which we contributed).

We'll probably tag for 3.9.0b1 and retarget the master branch to take that one, so that we can control updates that go into that release. But right now there isn't anything we want to tag right now (and GitHub generates the tarball itself, so we don't have to upload anything - you can get the branch tip through the "Download" button on the front page).