[OE-core] Looking for a way to build latest tagged releases in recipes

[chris.laplante at agilent.com]

> TODO:
> 
> * Right now, the class triggers a base environment change every time, which means BitBake always reparses every recipe. I guess this
> is because I'm modifying the datastore when I get bb.event.ConfigParsed and bb.event.MultiConfigParsed, in order to ensure
> REVRECORD_DATETIME is the same across all configurations when multiconfig is active. Perhaps there is a more elegant way to do
> this that won't trigger the environment change? To be fair I think in most cases you won't care, since I expect this class to mainly be
> used in a continuous integration environment where you'll be doing a clean build and having to reparse everything anyway. But I
> could also see this class a useful to thing to always have enabled, even for personal builds, and in that case obviously I'd want to fix
> this issue.
> * When multiconfig is active, I would also like a "global" revs.inc to be generated, which is the product of aggregated the "revs.inc" for
> all the multiconfigs. Still need to think about how exactly this will work in the face of conflicting SRCREVs.
> * We have a use case for JSON format data as well ("revs.json") - I'll add that too.
> * Possibly a small tinfoil script that simply automates the task of INHERIT'ing this class, parsing all the recipes, and then dumping
> revs.inc.

Cross the first TODO off the list: https://gist.github.com/mostthingsweb/39e24b329de70c0212e5bf21a431e143/8d1a5f51b3c0bf260c730ed5716d9807c78335b8

(BTW eventually I will move this to poky-contrib; gist is just more convenient for me for the short term. If there's a desire for it to happen sooner let me know.)

Chris