Using external libs

I intend to do a php extension with Zephir that wraps around libgit2 I know it already exists, but its in alpha state and in C, so I can't contribute to that without learning all the things needed to be a C dev, and I'm planning on using Zephir because of exactly that. That, and I pretend to do it OO as well.

How would I go about adding the dependency on libgit2 in my Zephir project?

Thanks!

Also, if I had a dependency to another extension, how would I go about doing that?