Add s390x docker build

[lysliu]

Fixes: #197

Update x.py add s390x by

@@ -21,6 +21,7 @@ debian_arches = [
 
 debian_non_buster_arches = [
     DebianArch("ppc64le", "ppc64el", "linux/ppc64le", "powerpc64le-unknown-linux-gnu"),
+    DebianArch("s390x", "s390x", "linux/s390x", "s390x-unknown-linux-gnu"),
 ]

debian_variants = [
then run

python3 x.py update

to update docker file

[Muscraft]

This looks fine to me, but I want to note that I have no way of testing s390x, so it will be supported on a best-effort case.

If you are up for getting pings when there are issues with s390x, please let me know! It would be appreciated.

[Muscraft]

docker-library/official-images#16676