Having build dependencies available as install dependencies

[rgommers (Ralf Gommers)]

@pradyunsg

I’ll concede that it’s functionality that isn’t implemented as of today in an accessible manner by any of the build backends today, but I also don’t see the need for every build backend (and more importantly, frontends like pip) to implement new functionality to support this usecase.

Yes, that is fair. Let me rephrase: it should be optional to implement, but for the backends that do implement such functionality, it seems preferable for them to all use the same syntax.