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

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um SHELL=/bin/bash drivers/mailbox/