reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/bcain/linux.git/commit/?id=8be2af9ea122e286ca475227495296847336bb9d
        git remote add bcain https://git.kernel.org/pub/scm/linux/kernel/git/bcain/linux.git
        git fetch --no-tags bcain bcain/qemu_boot
        git checkout 8be2af9ea122e286ca475227495296847336bb9d

        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # apt-get install sparse
        # sparse: v0.6.5-rc1

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=hexagon olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=hexagon SHELL=/bin/bash arch/hexagon/kernel/ dtbs