The LLVMLinux project and other related initiatives to build the Linux kernel with Clang instead of GCC have been discussed many times in the past on Phoronix: LLVM/Clang Is Advancing To Build The Linux Kernel, Building Linux With LLVM/Clang Excites The Embedded World, etc.
The state of the work is basically that x86/ARM builds of the Linux kernel can happen with Clang using a mostly un-patched version of the compiler but there's still numerous patches that have yet to be upstreamed on the kernel side. Even with the available patches, not all features of the Linux kernel are supported with the Clang-compiled kernel.
For those interested in more details on the project an update on LLVMLinux was shared this past weekend at FOSDEM. These slides cover the project by Jan-Simon Möller.