reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/bcain/linux.git/commit/?id=78951630122eae2f9915fda71077ecd729f34ff0
        git remote add bcain https://git.kernel.org/pub/scm/linux/kernel/git/bcain/linux.git
        git fetch --no-tags bcain bcain/boot_qemu
        git checkout 78951630122eae2f9915fda71077ecd729f34ff0

        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=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=hexagon olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash