Getting farther - after "hacking" pandas setup.py to not force a gcc flag.

Still not getting as far, I think, as the initial poster.

...
/opt/include/python3.8dm -c pandas/_libs/parsers.c -o build/temp.aix-6.1-3.8-pydebug/pandas/_libs/parsers.o
xlc_r -O -I/opt/include -O2 -qmaxmem=-1 -qarch=pwr5 -I/opt/include -O2 -qmaxmem=-1 -qarch=pwr5 -Ipandas/_libs/src/klib -Ipandas/_libs/src -I/opt/lib/python3.8/site-packages/numpy/core/include -I/opt/include/python3.8dm -c pandas/_libs/src/parser/tokenizer.c -o build/temp.aix-6.1-3.8-pydebug/pandas/_libs/src/parser/tokenizer.o
"/opt/include/python3.8dm/pyconfig.h", line 1538.9: 1506-236 (W) Macro name _POSIX_C_SOURCE has been redefined.
"/opt/include/python3.8dm/pyconfig.h", line 1538.9: 1506-358 (I) "_POSIX_C_SOURCE" is defined on line 160 of /usr/include/standards.h.
"/opt/include/python3.8dm/pyconfig.h", line 1553.9: 1506-236 (W) Macro name _XOPEN_SOURCE has been redefined.
"/opt/include/python3.8dm/pyconfig.h", line 1553.9: 1506-358 (I) "_XOPEN_SOURCE" is defined on line 156 of /usr/include/standards.h.
"/usr/include/unistd.h", line 171.17: 1506-343 (S) Redeclaration of lseek64 differs from previous declaration on line 169 of "/usr/include/unistd.h".
"/usr/include/unistd.h", line 171.17: 1506-050 (I) Return type "long long" in redeclaration is not compatible with the previous return type "long".
"/usr/include/unistd.h", line 171.17: 1506-377 (I) The type "long long" of parameter 2 differs from the previous type "long".
"/usr/include/sys/lockf.h", line 64.20: 1506-343 (S) Redeclaration of lockf64 differs from previous declaration on line 62 of "/usr/include/sys/lockf.h".
"/usr/include/sys/lockf.h", line 64.20: 1506-377 (I) The type "long long" of parameter 3 differs from the previous type "long".
"/usr/include/unistd.h", line 809.33: 1506-343 (S) Redeclaration of ftruncate64 differs from previous declaration on line 807 of "/usr/include/unistd.h".
"/usr/include/unistd.h", line 809.33: 1506-377 (I) The type "long long" of parameter 2 differs from the previous type "long".
"/usr/include/unistd.h", line 845.33: 1506-343 (S) Redeclaration of truncate64 differs from previous declaration on line 843 of "/usr/include/unistd.h".
"/usr/include/unistd.h", line 845.33: 1506-377 (I) The type "long long" of parameter 2 differs from the previous type "long".
"/usr/include/unistd.h", line 862.33: 1506-343 (S) Redeclaration of pread64 differs from previous declaration on line 859 of "/usr/include/unistd.h".
"/usr/include/unistd.h", line 862.33: 1506-377 (I) The type "long long" of parameter 4 differs from the previous type "long".
"/usr/include/unistd.h", line 863.33: 1506-343 (S) Redeclaration of pwrite64 differs from previous declaration on line 860 of "/usr/include/unistd.h".
"/usr/include/unistd.h", line 863.33: 1506-377 (I) The type "long long" of parameter 4 differs from the previous type "long".
"/usr/include/unistd.h", line 942.25: 1506-343 (S) Redeclaration of fclear64 differs from previous declaration on line 939 of "/usr/include/unistd.h".
"/usr/include/unistd.h", line 942.25: 1506-050 (I) Return type "long long" in redeclaration is not compatible with the previous return type "long".
"/usr/include/unistd.h", line 942.25: 1506-377 (I) The type "long long" of parameter 2 differs from the previous type "long".
"/usr/include/unistd.h", line 943.25: 1506-343 (S) Redeclaration of fsync_range64 differs from previous declaration on line 940 of "/usr/include/unistd.h".
"/usr/include/unistd.h", line 943.25: 1506-377 (I) The type "long long" of parameter 3 differs from the previous type "long".
"pandas/_libs/src/parser/tokenizer.c", line 265.40: 1506-280 (W) Function argument assignment between types "long long*" and "unsigned long*" is not allowed.
"pandas/_libs/src/parser/tokenizer.c", line 292.30: 1506-280 (W) Function argument assignment between types "long long*" and "unsigned long*" is not allowed.
"pandas/_libs/src/parser/tokenizer.c", line 323.28: 1506-280 (W) Function argument assignment between types "long long*" and "unsigned long*" is not allowed.
error: command 'xlc_r' failed with exit status 1
root@x066:[/data/prj/python/pandas-0.23.4]set | grep OBJ
root@x066:[/data/prj/python/pandas-0.23.4]python3
Python 3.8.0a0 (heads/master-dirty:b9498e2367, Nov 10 2018, 13:51:41) [C] on aix6
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.maxsize()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable
>>> sys.maxsize
2147483647

+++++
Will uninstall and build a 64-bit python3 and see if that helps.
+++++