In llvm-r1.eclass, llvm_prepend_path is called without any arguments other than the LLVM_SLOT. This causes build failures in gentoo prefix, as the PATH variable will now contain an absolute path into /usr, which may contain tools and configuration files with different options. I think the "prefix" variable in this function should be initialized to ${EPREFIX}, if not be disallowed from being called without specifying a prefixed option (I'm not 100% sure in what circumstances you want BROOT or ESYSROOT, respectively).
Worth noting is that in llvm-r2.eclass, the function is called with `-b`, so it might make sense to default on that. get_llvm_prefix() in llvm-r2.eclass has this same issue.
