For weeks there have been public talk by developers on the SPIR-V plans for LLVM. Today there is some fresh material after the involved developers have been communicating with The Khronos Group.
In their discussions they determined they need to create a "fully fledged" back-end that uses all of the LLVM machinery that target back-ends should use. They also determined they'd likely need to develop the SPIR-V to LLVM IR translator as a separate project, similar to Clang being technically separate from LLVM.
However, in wanting to get out SPIR-V code right now, they are going to open-source their current code shortly. This soon-to-be-opened code doesn't comply with the above criteria, but it's a start and will allow them to ship something soon. A full SPIR-V back-end to LLVM is then said to be revisited in the future.
Details via this mailing list post. The code is to appear on KhronosGroup GitHub.