Your question is overly broad. This is a large task, and you should be more specific about which part of the task you're seeking help with. Here are some pointers to existing projects you may want to look at:
- The LLVM C backend - generates C code back from LLVM IR. The caveat is that this backend was dropped following the 3.1 release so you'll have to look in the sources of earlier releases.
- Emscripten - generates Javascript from LLVM IR