According to an article on Phoronix by Michael Larabel, the coreboot project has been updated to support LLVM Clang, in addition to GCC. This is great news, having additional compilers target a project is good for finding errors, and LLVM has the klee fuzzer that might become useful with coreboot when used with a VM like QEMU.
More information:
http://www.phoronix.com/scan.php?page=news_item&px=Clang-Coreboot-Crossgcc