add MATLAB to GitHub Actions

[KrisThielemans]

@traversaro a reminder that you volunteered to add GHA support for MATLAB (see https://github.com/jaeandersson/swig/issues/96#issuecomment-903308358_). However, swig/master has had recent updates to the GHA workflow which aren't in #96 at present, so you probably want to hang a bit longer.

[traversaro]

@KrisThielemans thanks for the remainder! Feel free to let me know when you think that https://github.com/jaeandersson/swig/pull/96 is ready to be modified with MATLAB support in GitHub Actions.

[KrisThielemans]

I believe #96 is now ready for this, as I've merged swig/master again. However, I suggest that @jaeandersson first merges #96, and you create a separate PR for a few reasons:

• you could do a PR on mine, but we'd have a 4 levels of PRs
• sorting out GHA in my experience takes about 50 commits anyway, which would make the history of #96 a mess. A separate PR for GHA would allow a squash-merge.

Of course, I guess you could start with this already anyway. as you prefer

[jaeandersson]

Thanks and sorry for not staying on top of this. A bit overwhelmed with other work, a toddler and a baby at the moment. I've put aside time to work on this the second week of January.

[traversaro]

Work ongoing on https://github.com/traversaro/swig/pull/1 (temporary PR just to run the CI somewhere).

[traversaro]

After some iterations, the CI at https://github.com/traversaro/swig/pull/1 has the test working. Current open points:

• There are a lot of warnings like Warning: invalid MATLAB symbol '_val' (variable) during test
• The clean step is failing
• All the other languages compile with -Werror, but doing that in MATLAB fails with errors warning: ISO C90 forbids mixed declarations and code