None yet. What's currently blocking us badly is handling macros in the code for compilation. Like any decent Lisp program, arc2c makes quite a bit of use of macros.
Unfortunately macros require us to embed an Arc interpreter in the compiler itself, and we can't use the builtin 'eval because we don't want the macros under compilation to accidentally bash global functions/variables used by the compiler itself.
You'll have to contact sacado if you're interested in chipping in, we haven't figured out how to make a git on github publicly pushable.