Python binding clones TaskFlow from configure

[yurivict]

I am trying to create a FreeBSD port for Jet's Python binding.
However, it clones TaskFlow.
Network access during package build isn't allowed.

Best solution would be to only clone it when TaskFlow isn't installed in the system.
Or, alternatively, to use git submodule.

[yurivict]

And the same problem is with pybind11.