reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://github.com/krzk/linux/commit/4a8f97d3a420624cfd72ca8a2f6f5bbb68efa3a3
        git remote add krzk-github https://github.com/krzk/linux
        git fetch --no-tags krzk-github b4/sm8750-iris-dts
        git checkout 4a8f97d3a420624cfd72ca8a2f6f5bbb68efa3a3
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm64 SHELL=/bin/bash dtbs_check