Related to #1928

I am trying to install liquidhaskell, which requires z3 to build. I do not know how to supply this as a build input using haskell.nix. Adding it to extra-libraries in the cabal file does not help. I imagine there must be a simple way to tell haskell.nix to build this package with z3 available, but I could not figure out a way to do this that works from the documentation.