fix(sys-kernel/coreos-kernel) build in almost all kernel modules

This resolves the "xen fails to boot, so it falls back" problem of
getting out of sync with the kernel and the modules on the root
partitions.  Once kexec is working for xen, modules can be built again.
Merge pull request #194 from gregkh/kernel_update

fix(sys-kernel/coreos-kernel) build in almost all kernel modules