reproduce (this is a W=1 build):
        git remote add klassert-ipsec-next https://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec-next.git
        git fetch klassert-ipsec-next master
        git checkout klassert-ipsec-next/master
        b4 shazam https://lore.kernel.org/r/20240219085735.1220113-9-chopps@chopps.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 SHELL=/bin/bash