[3.14] gh-141004: Document remaining `pyport.h` utility macros (GH-144279) (GH-144477)

gh-141004: Document remaining `pyport.h` utility macros (GH-144279)
(cherry picked from commit 914fbec21458a0344468734489f29254033fafc5)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>