Extract of David Edelsohn's email:
"""
The testsuite failures on AIX are issues with the AIX kernel and C
Library, often corner cases.  I don't want to get into arguments about
the POSIX standard.  Some of the issues are actual conformance issues
and some are different interpretations of the standard.  Addressing
the problems in AIX is a slow process. If the failing testcases are
too annoying, I would recommend to skip the testcases.

Despite the testsuite failures, Python builds and runs on AIX for the
vast majority of users and applications.  I don't see the benefit in
dropping support for a platform that functions because it doesn't
fully pass the testsuite.
"""
ref: https://mail.python.org/pipermail/python-dev/2017-April/147748.html

I agree, so let's skip tests known to fail on AIX!