reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://github.com/sean-jc/linux/commit/56a5a2c6595dea5e793bc5b6d1a9198a52b9ede9
        git remote add sean-jc https://github.com/sean-jc/linux
        git fetch --no-tags sean-jc x86/mediated_pmu
        git checkout 56a5a2c6595dea5e793bc5b6d1a9198a52b9ede9
        # 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