reproduce (this is a W=1 build):
        mkdir -p ~/bin
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install arm64 cross compiling tool for clang build
        # apt-get install binutils-aarch64-linux-gnu
        # https://github.com/AsahiLinux/linux/commit/dcf43a427ffcbc79686412189e790ae5f406b748
        git remote add asahilinux https://github.com/AsahiLinux/linux
        git fetch --no-tags asahilinux bits/020-dart
        git checkout dcf43a427ffcbc79686412189e790ae5f406b748
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=arm64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=arm64 SHELL=/bin/bash arch/arm64/kernel/ drivers/iommu/ drivers/phy/