One of the core contributors here. The trick is that Avian doesn't do JIT compilation on iOS - instead, we run everything through the "JIT" compiler ahead of time, as we're building the app. This is the only possible technique, outside of interpretation (which Avian can also do, but slowly), and compiling to Javascript to run with JavascriptCore. It's also what I've seen most other VMs do for iOS (including, for instance, the Unity game engine, which used to embed Mono).
