reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=93f78dadee5e56ae48aff567583d503868aa3bf2
        git remote add tip https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
        git fetch --no-tags tip x86/alternatives
        git checkout 93f78dadee5e56ae48aff567583d503868aa3bf2
        # 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 prepare