For some reason diffutils is not included in the Fedora containers anymore,
causing the build to fail.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20201003085054.332992-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>