How to get the source code of FreeBSD-Clang?

[Yue Chen]

When I use the original versions (even 3.4.1) of LLVM/Clang to compile
FreeBSD kernel, it always has problems.

Since I need to modify something in LLVM source and then build the kernel,
where can I get the FreeBSD-friendly Clang/LLVM source code?

Thanks.