reproduce (this is a W=1 build):
        # https://github.com/morimoto/linux/commit/2b4bb2b272501af9302a01713e7e35ec89d1297a
        git remote add morimoto https://github.com/morimoto/linux
        git fetch --no-tags morimoto renesas-lts/v6.18-rc6-2025-11-20-x5h-ironhide-2
        git checkout 2b4bb2b272501af9302a01713e7e35ec89d1297a

        # install um cross compiling tool for clang build
        # apt-get install binutils-um-linux-gnu
        # clang-22 might not be officially released. Try a lower version if installation fails.
        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=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-22 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um SHELL=/bin/bash drivers/mailbox/