(CLJS) go block containing letfn does not compile
Description
The following compiles and runs correctly:
However, this fails to compile with `clojure.lang.ExceptionInfo: bindings must be vector of even number of elements...`:
Environment
[org.clojure/clojure "1.8.0-RC3"]
[org.clojure/clojurescript "1.7.189"]
[org.clojure/core.async "0.2.374"]
