ci: Compile with minimum supported g++ in olddeps

[maflcko]

Looks like there is no CI coverage for the minimum supported g++ version?

[DrahtBot]

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

Reviews

See the guideline and AI policy for information on the review process.

Type	Reviewers
ACK	ryanofsky

If your review is incorrectly listed, please copy-paste <!--meta-tag:bot-skip--> into the comment that the bot should ignore.

Conflicts

Reviewers, this pull request conflicts with the following ones:

• #175 (Set cmake_minimum_required(VERSION 3.22) by maflcko)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

[hebasto]

ci: Compile with minimum supported g++-11 in olddeps

It seems g++10 is the minimum supported.

[ryanofsky]

Code review ACK edf6343. Would maybe change title to "Compile with older GCC in olddeps" because it's not clear what the real minimum is. (Or if it is clear it would be nice to document).

Also this is only testing libmultiprocess build with the older GCC, so using older GCC for capnproto as well could be more realistic, but this PR is probably the simplest change

[maflcko]

Would maybe change title to "Compile with older GCC in olddeps" because it's not clear what the real minimum is. (Or if it is clear it would be nice to document).

Happy to do this, but not sure how. Should I cherry-pick bitcoin/bitcoin#34580 into this repo ?

Also this is only testing libmultiprocess build with the older GCC, so using older GCC for capnproto as well could be more realistic, but this PR is probably the simplest change

This seems like something for upstream to do. Recall they already have Linux-old (g++-9) config.