refactor: Improve and align Makefiles

[gibson042]

Can be reviewed commit-by-commit or all at once.

Future work may merge the four Makefiles into a pair or even just one file.

[mhofman]

FYI I have been avoiding making too many changes to the makefiles to avoid conflicts with the fork @phoddie maintains, or diverging from the Makefiles of the Moddable repo itself, changes to which we usually need to reflect here.

[gibson042]

FYI I have been avoiding making too many changes to the makefiles to avoid conflicts with the fork @phoddie maintains

That seems to be the only fork, so I think we can reconcile.

or diverging from the Makefiles of the Moddable repo itself, changes to which we usually need to reflect here.

Can you elaborate? If we're considering other files to be essentially upstream, I'd like to document that here.

[mhofman]

Can you elaborate? If we're considering other files to be essentially upstream, I'd like to document that here.

My understanding is that these makefiles were started as copies of https://github.com/Moddable-OpenSource/moddable/tree/public/xs/makefiles (or more precisely their ancestors). When upgrading XS version it often involves replicating changes made to these makefiles (amongst other things)