Migrate to Github Actions CI

[offa]

Adds Github Actions CI and removes (no longer available) Travis CI.

This includes additional builds of latest Clang and GCC version with C++20 enabled.

Preparatory work

This is a draft since these two PRs are necessary to get a green build:

• Workaround GCC 12 warning #2498
• Workaround deprecation warning on Clang with C++20 #2499

I'll rebase this PR once these two are merged.

[offa]

PR rebased 👍

[gabime]

Thanks @offa.
The thing is, that I lack the time for learning and/or supporting Actions CI.
If you have the time to support this, it would be great, otherwise I will have to pass.

[offa]

Yes, let me know if there's something to do!

[gabime]

Well for starters we need to replace the travis status icon with the Actions CI icon in readme.md

[offa]

Seems I have missed that … 😆

Badge is updated and should become visible once Actions are active on the default branch.

[gabime]

Whats the teeks99 line do?

matrix.config.compiler == 'clang' && 'teeks99/clang-ubuntu'

[offa]

It selects the teeks99/clang-ubuntu docker image on Clang builds. GCC builds use the gcc image.

[gabime]

why this particular image? seems like pretty obscure docker image. I hope we can live without it

[offa]

Unlike GCC, there's no official Clang image (AFAIK). There are other images around, but that one works quite nice on CI, is based on Ubuntu, provides almost all version of Clang and is widely used.

I hope we can live without it

We could, but then we have to do all the work manually. In case where needed version of clang isn't shipped by the Actions runner, it'll become quite an effort.

[gabime]

Thanks @offa . Looking good so far.