test_threading has a similar issue, still on PPC64 AIX 3.x:
https://buildbot.python.org/all/#builders/10/builds/3171

test_recursion_limit (test.test_threading.ThreadingExceptionTests) ... FAIL
test_releasing_unacquired_lock (test.test_threading.ThreadingExceptionTests) ... ok
test_start_thread_again (test.test_threading.ThreadingExceptionTests) ... ok
test_init_immutable_default_args (test.test_threading.TimerTests) ... ok

======================================================================
FAIL: test_recursion_limit (test.test_threading.ThreadingExceptionTests)
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Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.aixtools-aix-power6/build/Lib/test/test_threading.py", line 1088, in test_recursion_limit
    self.assertEqual(p.returncode, 0, "Unexpected error: " + stderr.decode())
AssertionError: -11 != 0 : Unexpected error:

----------------------------------------------------------------------

Ran 168 tests in 12.623s

FAILED (failures=1)
Warning -- files was modified by test_threading
  Before: []
  After:  ['core']