Was:
root@x064:[/data/prj/python/python3-3.8]./python
Python 3.8.0a3+ (heads/bpo-28009-2-dirty:2fb2bc81c3, Apr 11 2019, 07:09:55) [C] on aix6
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.platform
'aix6'
>>> import os
>>> os.uname()[3]
'7'

./python ../git/python3-3.8/Tools/scripts/patchcheck.py
Getting base branch for PR ... origin/master
Getting the list of files that have been added/changed ... 6 files
Fixing Python file whitespace ... 0 files
Fixing C file whitespace ... 0 files
Fixing docs whitespace ... 0 files
Docs modified ... yes
Misc/ACKS updated ... NO
Misc/NEWS.d updated with `blurb` ... yes
configure regenerated ... yes
pyconfig.h.in regenerated ... no

On system I built on:
root@x066:[/data/prj/python/python3-3.8]./python
Python 3.8.0a3+ (heads/bpo-36588-aix-platform-dirty:2021d40faa, Apr 11 2019, 15:16:05) [C] on aix
Type "help", "copyright", "credits" or "license" for more information.
>>> import os,sys
>>> sys.platform
'aix'
>>> os.uname()[3]
'6'

And on AIX7 system:
root@x064:[/data/prj/python/python3-3.8]./python
Python 3.8.0a3+ (heads/bpo-36588-aix-platform-dirty:2021d40faa, Apr 11 2019, 15:16:05) [C] on aix
Type "help", "copyright", "credits" or "license" for more information.
>>> import os,sys
>>> sys.platform
'aix'
>>> os.uname()[3]
'7'