[BPT] Header only libs have limited job matrix.

[grafikrobot]

Description of Problem, Request, or Question

The job matrix generated by BPT for header only libraries seems to only contain four builds: Linux release+debugs, and Windows release+debug. They..

• Are unlabeled "generic" build, i.e. without compiler, architecture, etc.
• Do not include MacOS with Xcode.

Package and Environment Details (include every applicable attribute)

• Conan version: Conan 1.36.0
• Python version: Python 3.9.4

[Croydon]

What are you trying to archive with that? Adding all potential build jobs for header_only does not seem reasonable I think 🤔

[grafikrobot]

The issue is that some header only libraries have per configuration definitions and linking requirements. And outside of one person locally testing all those requirements CI is the only other way to check that they work. For example the olc-pge library that I've been trying to get into CCI https://github.com/conan-io/conan-center-index/pull/5283. Which I'm now trying to provide outside of CCI https://github.com/bfgroup/conan/actions/runs/803704935. In those bfgroup/conan results I hacked BPT to do the full matrix https://github.com/bincrafters/bincrafters-package-tools/commit/6cedbee74d9fe7ba3fd49aaa8df2ea2177852b39.