CI improvements: add macOS runners; build in parallel; disable silent rules

[ryandesign]

This adds a few more improvements to the CI setup:

• adds macOS runners (these will currently fail due to #1495)
• builds in parallel for improved speed
• disables silent rules for improved logging

See the individual commit messages for more specifics.

Fixes #1496

[linas]

I've merged all the other pull reqs, hit the "rerun all tests" button on github, and the macos tests are still failing. I don't particularly want to merge this, until those tests pass.

Perhaps a git merge master is needed into this branch?

[ryandesign]

I've rebased this PR and now instead of failing at make due to #1495 it fails as expected at make check due to #1514.

If a fix for #1514 is not easy, I can, if you like, modify the macOS CI so that it doesn't use pcre2 for now.

[linas]

Hi @ryandesign I replied to #1514 The fix is not hard, and if you ever wanted to learn threading, this would be an excellent starter project. In the meantime, for macos CI, either disable the multi-threading tests or disable testing pcre2. Your pick. The command-line link-parser program is not multi-threaded; users would never notice. OpenCog is heavily multi-threaded, which is where this matters, to me. As far as I know, there's no port of OpenCog to Macos. Want to engage in a crazy-stupid and pointless project?