Comment 9 for bug 1921468

I spoke to cborntra, and it turned out that this affects only guests with zipl
with: 86856f98 "zipl: Make use of __noreturn macro"
but not yet: c367a6bb "zipl/libc: libc_stop move 'noreturn' to declaration"

That means 2.12/2.13 and that translates to Focal.
Therefore retry this as:

ubuntu@s1lp5:~$ virt-install --name testinst2 --memory 2048 --disk path=/dev/disk/by-path/ccw-0.0.151e --cdrom /var/lib/libvirt/images/ubuntu-20.04-legacy-server-s390x.iso
- all defaults -
- install as "entire disk -

Then on reboot I get still what seems working:

```
The system is going down NOW!
Sent SIGTERM to all processes
Sent SIGKILL to all processes
Requesting system reboot

Domain creation completed.ts; <Enter> activates buttons
Restarting guest.
Connected to domain testinst2
Escape character is ^]

Booting entry #0
```

We talked further and it is also compiler specific.
Eventually any guest "could" fail and it definitely is wise to fix this.
Just verification gets harder.

I'll try some other ISOs as instructed by Christian to see if one can be used as repro case.