reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # clang-22 might not be officially released. Try a lower version if installation fails.
        git remote add batman https://git.open-mesh.org/linux-merge.git
        git fetch --no-tags batman batadv/net-next
        git checkout db615ccdc9bd480fd632f16b9ff5dcf340430f44
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=hexagon olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash net/batman-adv/