[WIP] Improved esy support

[rauanmayemir]

This PR streamlines the structure towards less hardcoded and more 'esy-way'. ninja-build and ocaml are dependencies, not vendor dumps.

[bsansouci]

Hey thanks for opening this. I really appreciate the help. That said I'd like to merge the esy branch inside master, so it's easier to maintain and I can actually dogwood it. For that, I need to keep the same vendored ocaml (and might as well keep ninja). I need it for JS compilation.

I'll merge the esy.json though, if that works :)

[rauanmayemir]

As long as it brings esy and bsb closer, no worries.

[chenglou]

yes please!

[bsansouci]

Heyyy how's this going? I'd love to get the esy.json merged since it's probably more correct than mine. Did you need to change anything inside bsb that makes the integration better?

[rauanmayemir]

Hey! Sorry, I didn't realise you meant merge esy.json from this PR.
Let me clean up unused commits and check that it actually works.

I need to keep the same vendored ocaml

Do you mean the old 4.02?

[bsansouci]

No worries! Awesome, thank you so much.

Yeah, for now keeping 4.02.3. I'll address that problem later.