sadly, this doesn't seem to support any sort of multithreading. Even something as simple as swap! isn't thread-safe in this implementation. So that kills one of the main reasons to use Clojure in the first place.
Lack of multithreading seems like a result of the implementation being heavily based on ClojureScript ;) (it's actually pretty cool to see how reusable core.cljs is IMO). I imagine ClojureC will have its uses like ClojureScript does when the JVM is not an option.