Improve amd64 detection on sunos

[github at samba.org]

New comment by abartlet on Samba Github repository

https://github.com/samba-team/samba/pull/208#issuecomment-446886170
Comment:
I'm sorry for the long delay in dealing with this.  To merge this into master this will need to work with python3, and I expect some bytes and strings issues (POpen and things that wrap it return bytes).

Also, it looks like this no longer applies on master.

Ideally you would re-open it on our GitLab instance, where we now do our web-based work, but if you could fix those issues and (most importantly) re-test on a SunOS system that would be most helpful.