You’re waiting for this issue I think - now llvm 3.7 has been released there’s no need to engage in svn checkout madness, musl rust can theoretically be set up as a first-class target on the buildbots. It’s also now even easier to build your own!
Unfortunately the rust buildbots are not fully documented so it’s a little tricky if you were to want to help - I understand it’s on a todo list.