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/sj/linux.git/commit/?id=607a455e2f3d528b71be200e1e18e578273a602e
        git remote add sj https://git.kernel.org/pub/scm/linux/kernel/git/sj/linux.git
        git fetch --no-tags sj mm-new
        git checkout 607a455e2f3d528b71be200e1e18e578273a602e
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash