Add Windows and macOS CI with GitHub actions

[msimberg]

Currently builds all tests, examples, etc. on macOS (and runs the tests). On Windows it only builds and runs the examples because of broken pseudo-dependencies.

This also fixes compilation of some more examples. I will cherry-pick those onto the release branch.

[hkaiser]

Nice! Thanks!

[msimberg]

Btw, the latest builds are here: macOS and Windows. In the previous round the macOS tests were pretty good (meaning around 10 failed tests). Some were affinity related and some not. On the Windows builder there are apparently only 2 PUs available, hence the new option HPX_WITH_TESTS_MAX_THREADS_PER_LOCALITY. The build is still running so not sure if it works yet.

[msimberg]

I'm also hoping that the status checks will start showing up once this is merged. If not I'll look into them separately.

[msimberg]

@hkaiser do any of these test failures look like something we would expect on Windows under normal conditions: https://github.com/msimberg/hpx/runs/444043594?check_suite_focus=true#step:6:8? Or would you guess that these are caused by limitations of running on a VM?

[hkaiser]

do any of these test failures look like something we would expect on Windows under normal conditions: https://github.com/msimberg/hpx/runs/444043594?check_suite_focus=true#step:6:8? Or would you guess that these are caused by limitations of running on a VM?

Frankly, I don't know what could have caused this.

[msimberg]

do any of these test failures look like something we would expect on Windows under normal conditions: https://github.com/msimberg/hpx/runs/444043594?check_suite_focus=true#step:6:8? Or would you guess that these are caused by limitations of running on a VM?

Frankly, I don't know what could have caused this.

No worries, then we'll live with them for now. I may add a blacklist of examples that we know fail to not miss newly introduced failures. I think the most important thing is that we at least build all the examples now.

[msimberg]

I'll merge this now and keep iterating once I see how it works on master.