kexectools: fix build on i686

https://hydra.nixos.org/build/99957229
See: https://src.fedoraproject.org/rpms/kexec-tools/c/cb1e5463b5298b064e9b6c86ad6fe3505fec9298

Forward-cherry picked from commit dc051dfd, but only conditionally
for i686 to rebuild only where necessary.  Discussion: PR #68380.