reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git/commit/?id=2b9c2213630da8f6f2a256005f9ce9070e39847f
        git remote add tj-sched-ext https://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git
        git fetch --no-tags tj-sched-ext scx-bypass-scalability-v2
        git checkout 2b9c2213630da8f6f2a256005f9ce9070e39847f

        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arc SHELL=/bin/bash kernel/