reproduce (this is a W=1 build):
        # https://github.com/jgunthorpe/linux/commit/e7b7ae31414a4f3db3fecb2bab0a2f101fff1bcf
        git remote add jgunthorpe https://github.com/jgunthorpe/linux
        git fetch --no-tags jgunthorpe fwctl
        git checkout e7b7ae31414a4f3db3fecb2bab0a2f101fff1bcf
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash