After a checkout the build finishes (successfully) with:
Python build finished successfully!
The necessary bits to build these optional modules were not found:
_gdbm                 _lzma                 _sqlite3
_tkinter              _uuid                 readline
To find the necessary bits, look in setup.py in detect_modules() for the module's name.


The following modules found by detect_modules() in setup.py, have been
built by the Makefile instead, as configured by the Setup files:
_abc                  atexit                pwd
time

running build_scripts
creating build/scripts-3.9
copying and adjusting /data/prj/python/git/python3-3.9/Tools/scripts/pydoc3 -> build/scripts-3.9
copying and adjusting /data/prj/python/git/python3-3.9/Tools/scripts/idle3 -> build/scripts-3.9
copying and adjusting /data/prj/python/git/python3-3.9/Tools/scripts/2to3 -> build/scripts-3.9
changing mode of build/scripts-3.9/pydoc3 from 644 to 755
changing mode of build/scripts-3.9/idle3 from 644 to 755
changing mode of build/scripts-3.9/2to3 from 644 to 755
renaming build/scripts-3.9/pydoc3 to build/scripts-3.9/pydoc3.9
renaming build/scripts-3.9/idle3 to build/scripts-3.9/idle3.9
renaming build/scripts-3.9/2to3 to build/scripts-3.9/2to3-3.9
/opt/bin/install -c -m 644 ../git/python3-3.9/Tools/gdb/libpython.py python-gdb.py
xlc_r -c  -DNDEBUG -O -I/opt/include -O2 -qmaxmem=-1 -qarch=pwr5 -I/opt/include -O2 -qmaxmem=-1 -qarch=pwr5    -I../git/python3-3.9/Include/internal -IObjects -IInclude -IPython -I. -I../git/python3-3.9/Include -I/opt/include -I/op
t/include  -DPy_BUILD_CORE -o Programs/_testembed.o ../git/python3-3.9/Programs/_testembed.c
../git/python3-3.9/Modules/makexp_aix Modules/python.exp . libpython3.9.a;  xlc_r /opt/lib/libintl.a -L/opt/lib -liconv -lexpat /opt/lib/libintl.a -L/opt/lib -liconv -lexpat   -Wl,-bE:Modules/python.exp -lld -o Programs/_testembed
Programs/_testembed.o libpython3.9.a -lintl -ldl  -lm   -lm
sed -e "s,@EXENAME@,/opt/bin/python3.9," < ../git/python3-3.9/Misc/python-config.in >python-config.py
LC_ALL=C sed -e 's,\$(\([A-Za-z0-9_]*\)),\$\{\1\},g' < Misc/python-config.sh >python-config

root@x065:[/data/prj/python/python3-3.9]./python
Python 3.9.0a4+ (tags/v3.9.0a4-59-gdffe4c0709-dirty:dffe4c0709, Mar 11 2020, 17:09:06) [C] on aix
Type "help", "copyright", "credits" or "license" for more information.
>>>