Compiling LLVM/Clang for iOS

I'm having some troubles getting LLVM compiled for the ARM iOS platform: what I'm trying to achieve is a on-device compiler for C, C++ and possibly ObjC.

I tried multiple times to compile it, both using Makefiles and the Xcode project generated from CMake. In the first case the compilation failed with a lipo error that said "no input file specified" related to compiler-rt.a, and the compiler-rt.a indeed doesn't exist in the path specified. In the second case Xcode has issues finding the crt/* headers and the compilation fails pretty early.

My build system is composed of Xcode 4.5.2 (should be LLVM 3.1) and the iOS SDK 6.0.

Thank you for your help,