Comment 0 for bug 1891877

Upstream has completed the 4.2.1 stable tag
  https://github.com/qemu/qemu/releases/tag/v4.2.1

Fixes are in groovy already via qemu 5.0

These are only non-feature backports, the majority this time being memleaks and bad accesses of some sort.

Some of the patches are already present in Ubuntu's 4.2 as of today.
But adding the others will serve the stability of our most recent LTS.