ci: Add test build in s390x to verify BE behavior

Most of drivers supports both endiannesses but we do not test this so
let's add a CI job to verify this

.gitlab-ci/libfprint-image-variables.yaml

@@ -1,2 +1,2 @@
 variables:
-  LIBFPRINT_IMAGE_TAG: v6
+  LIBFPRINT_IMAGE_TAG: v8

.gitlab-ci/libfprint-templates.yaml

@@ -27,6 +27,8 @@
     meson
     openssl-devel
     pixman-devel
+    podman
+    qemu-user-static
     python3-cairo
     python3-gobject
     systemd

.gitlab-ci/qemu-user-static/container-entrypoint

@@ -0,0 +1,27 @@
+#!/bin/sh
+#
+# Unregister any stale qemu-*-static binfmt handlers and (re-)register the ones
+# shipped by this image via systemd-binfmt, so the host always uses the recent
+# qemu-user-static built into this image (registered with the "F" fix-binary
+# flag from /usr/lib/binfmt.d).
+#
+# Based on https://www.itix.fr/blog/qemu-user-static-with-podman/
+
+set -Eeuo pipefail
+
+if [ ! -d /proc/sys/fs/binfmt_misc ]; then
+    echo "No binfmt support in the kernel."
+    echo "  Try: '/sbin/modprobe binfmt_misc' from the host"
+    exit 1
+fi
+
+if [ ! -f /proc/sys/fs/binfmt_misc/register ]; then
+    echo "Mounting /proc/sys/fs/binfmt_misc..."
+    mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc
+fi
+
+echo "Cleaning up..."
+find /proc/sys/fs/binfmt_misc -type f -name 'qemu-*' -exec sh -c 'echo -1 > {}' \;
+
+echo "Registering..."
+exec /usr/lib/systemd/systemd-binfmt