Docker image building improvements

[stickz]

1. Instead of building all the platforms at once, build them as a separate jobs.
2. Build c-ares and curl with cmake to significantly speed along the build process.
3. Disable build warnings for xmlrpc, libtorrent and rtorrent to speed along the build process.
4. Fixed a critical issue where xmlrpc and libtorrent was not being built with the intended flags.

This should resolve timeout problems for PRs.

[stickz]

@crazy-max I was unable to test my changes in #291 due to GitHub Actions time-outs. So I made you a brand new workflow for GitHub pull requests, built c-ares and curl with cmake and disabled gcc warnings during build for some software.

[stickz]

Sorry about all that building. When I separated the tasks and silenced warnings, I saw the rTorrent software stack was not building with the intended flags. Everything is fixed now. We have 5m feedback for x86 and 40m feedback for ARM.

The build process for ARM has also been significantly optimized to cut down on time. There is less verbose and c-ares + curl is built with a much more efficient cmake process.

These changes will make it much easier to develop/maintain the docker container. Everything is working fast and flawlessly now.

[crazy-max]

I will make some changes to distribute builds across runners. I already done this in https://github.com/crazy-max/docker-linguist/blob/master/.github/workflows/build.yml based on a guide I made: https://docs.docker.com/build/ci/github-actions/multi-platform/#distribute-build-across-multiple-runners

I keep you posted.

[stickz]

Thanks! I will submit a new pull request in 15 minutes!

[crazy-max]

Merged #293 and opened #294 as follow-up to fix some issues.