Unfortunately, LLVM is very heavily oriented toward register machines, so adapting its backends to handle a stack architecture would be quite onerous. There is, however, a forth-like demo language called Stacker[1] which might interest you.
edit: It's also worth noting that .fs (Forth Source) has quite a bit of history as a Forth file extension. Github is of the opinion that this belongs to F#, much to my chagrin.
edit: It's also worth noting that .fs (Forth Source) has quite a bit of history as a Forth file extension. Github is of the opinion that this belongs to F#, much to my chagrin.
[1] http://llvm.org/releases/2.0/docs/Stacker.html