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/anna-maria/linux-devel.git/commit/?id=1f2cec28b82b702d8baeb95bb9b66061e876d6c5
        git remote add anna-maria-devel https://git.kernel.org/pub/scm/linux/kernel/git/anna-maria/linux-devel.git
        git fetch --no-tags anna-maria-devel vdso/cleanup
        git checkout 1f2cec28b82b702d8baeb95bb9b66061e876d6c5
        # 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 prepare