With Linux 3.15 came the patch-set to come close to being able to compile under Clang and now with Linux 3.16 it's a bit closer. A set of five LLVMLinux patches are called for merging that affect ARM and Shash Crypto code.
Behan Webster sent in the 3.16 pull request on Saturday, "Next set of patches to support compiling the kernel with clang. They've been soaking in linux-next since the last merge window. More still in the works for the next merge window..."
In case you missed it, a few days back I ran benchmarks covering Building The Linux Kernel With LLVM's Clang Yields Comparable Performance against the GNU Compiler Collection.