Following the 2022-03-05 SG15 telecon, I decided to make an attempt at
describing the various build system scenarios we've been discussing.
Please see the following Google doc.

  * https://docs.google.com/document/d/1JWW7Q-94nx6ObpupePkA2NAER7rylJQZpw4t755aeZQ/edit?usp=sharing

Please feel free to edit the doc or add comments to it; the doc is
publicly shared.

I know Google Docs is not convenient or even accessible to everyone. If
you are not able to view the doc, let me know and I'll send a copy as an
attachment. For now, I'm hoping that collaborative editing will help
fill in gaps and correct mistakes and misunderstandings.

The solution sections are vague and, for the last scenario, probably
unrealistic. I just wanted to include something as a starting point.

Tom.