So, with the patch - the process stops at:

aixtools@x064:[/home/aixtools/python-3.9]make
 CC='xlc_r' LDSHARED='Modules/ld_so_aix xlc_r -bI:Modules/python.exp    ' OPT='-DNDEBUG -O'  _TCLTK_INCLUDES='' _TCLTK_LIBS=''  ./python -E ./setup.py  build
Traceback (most recent call last):
  File "/home/aixtools/python-3.9/Lib/subprocess.py", line 72, in <module>
    import msvcrt
ModuleNotFoundError: No module named 'msvcrt'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/aixtools/python-3.9/./setup.py", line 4, in <module>
    import subprocess
  File "/home/aixtools/python-3.9/Lib/subprocess.py", line 77, in <module>
    import _posixsubprocess
ModuleNotFoundError: No module named '_posixsubprocess'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/aixtools/python-3.9/./setup.py", line 16, in <module>
    sys.modules['subprocess'] = _bootsubprocess
NameError: name 'sys' is not defined
make: 1254-004 The error code from the last command is 1.


Stop.