Bug#963054: Mark two more symbols as optional when building with -march=z13 on s390x

[Matthias Klose]

Package: src:gringo
Version: 5.4.0-2
Severity: important
Tags: sid bullseye patch

Mark two more symbols as optional when building with -march=z13 on s390x.

patch at
http://launchpadlibrarian.net/484809497/gringo_5.4.0-2_5.4.0-2ubuntu1.diff.gz