ubuntu-trusty 14.04 is long past "standard support" and will reach its EOL in April 2022 (https://wiki.ubuntu.com/Releases), but several optional packages do not build on it because of an outdated compiler (gcc 4.x)

debian-jessie (8) is past EOL LTS, with EOL ELTS in June 2022 (https://wiki.debian.org/DebianReleases). Same situation with gcc 4.x.

linuxmint-17 is past EOL (https://forums.linuxmint.com/viewtopic.php?t=289281). gcc 4.x

centos-7 has EOL June 2024. gcc 4.x

We switch these systems in the GH Actions CI tests for optional packages to using the gcc_spkg configuration factor.

Next wave:

• linuxmint-18 with gcc 5.4
• slackware-14.2 with gcc 5.5

Depends on #29527

CC: @kliem @dimpase

Component: porting

Author: Matthias Koeppe

Branch/Commit: 17ca365

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/31526