reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/cip/linux-cip.git/commit/?id=e30081fa5b814f5557b6fbd6e73f0cb504f67cbf
        git remote add cip https://git.kernel.org/pub/scm/linux/kernel/git/cip/linux-cip.git
        git fetch --no-tags cip linux-4.19.y-cip-rt-rebase
        git checkout e30081fa5b814f5557b6fbd6e73f0cb504f67cbf
        # 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 SHELL=/bin/bash net/ipv4/ net/xfrm/