Setup LLVM crosscompiler on XCode 4.3 for various platforms

I need to have a working LLVM/CLANG cross compiler setup to be used in XCode 4.3. According to my research the shipped LLVM/CLANG can already produce binaries for other platforms such as Linux/ELF but it needs the correct flags and binary files (for example crt1.o etc..) to create the correct binaries. I need to have this tested out and to produce a corresponding compiler definition file so compiling a foreign code out of xcode would simply mean duplicating the target and changing from CLANG for Mac to a "Clang compiler for Platform XYZ" I need this for the following platforms CentOS 5.3 i386 CentOS 5.3 x86_64 CentOS 5.7 i386 (might be same as 5.3) CentOS 5.7 x86_64 CentOS 6.2 i386 CentOS 6.2 x86_64 Ubuntu Server 10.04 LTS i386 Ubuntu Server 10.04 LTS x86_64 Ubuntu Server 11.10 i386 Ubuntu Server 11.10 x86_64 Ubuntu Server 11.10 for ARM FreeBSD 8.2 i386 FreeBSD 8.2 amd64 FreeBSD 8.2 ia64 FreeBSD 8.2 powerpc FreeBSD 8.2 powerpc64 FreeBSD 8.2 sparc64 FreeBSD 9.0 i386 FreeBSD 9.0 amd64 FreeBSD 9.0 ia64 FreeBSD 9.0 powerpc FreeBSD 9.0 powerpc64 FreeBSD 9.0 sparc64 OpenSolaris 11 x86 OpenSolaris 11 SPARC SunOS 5.8 (Solaris 8) on Sparc (sun4u) Android on ARM