Ubuntu 21.10 and 20.04.3

Ubuntu 21.10 "Impish Indri" is also out, upgrading to kernel 5.13, GNOME 40 (but presumably past the teething pains in Fedora 34 which required later patching) and gcc 11. This is the last interim release before the next Ubuntu LTS, scheduled for April 2022; the current LTS is updated to 20.04.3. As usual, new installs on OpenPOWER require installing Ubuntu Server first, and then converting to Desktop.