reproduce (this is a W=1 build):
        git remote add masahiroy-kbuild https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
        git fetch masahiroy-kbuild kbuild
        git checkout masahiroy-kbuild/kbuild
        b4 shazam https://lore.kernel.org/r/20240611175536.3518179-7-masahiroy@kernel.org
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 olddefconfig