do_cmake.sh: fedora-32 (rawhide) build with python-3.8
Fedora-32 now has python-3.8.
Fedora-29 is EOL. All non-EOL versions of Fedora have python-3.7, except
(Unclear to me why PYBUILD="3" isn't used, like Ubuntu and FreeBSD. That
would eliminate breakage when pyhon versions change in Rawhide.)