How do you use a non-dmd compiler within dub as default compiler?

[Jamal via Digitalmars-d-learn]

I made this little sdl2 game and written in D, and the project 
was initialized with dub.

When in the project directory and I type:

$ dub

It fetches all the dependencies and compiles with dmd.

So, what do I chance so that instead it compiles with ldc2 or 
even gdc for that matter?