reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git/commit/?id=a5027b86a79716e98fe0b8e1247743dfb5a5c080
        git remote add viro-vfs https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git
        git fetch --no-tags viro-vfs work.fd
        git checkout a5027b86a79716e98fe0b8e1247743dfb5a5c080
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
        ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash arch/powerpc/platforms/cell/