JamPlus

I don't know of any yet. I would have got it going myself, but Xcode 4 just does not want to work 'right' for me. See the other Xcode 4 forum posting.

I was digging around with some of the llvm stuff, and it looks like they included a nice llvm frontend that looks like gcc to the command line.

Looks like you can just replace
gcc-4.2, gcc++-4.2 in the iphone-gcc.jam file with
llvm-gcc and llvm-gcc++

I made the change and rebuilt, and it seems to compile fine (and a touch faster)

Dunno what the resultant code is like though - I still haven't gotten my project to the point where it can run