Add Extra Build Tools to Haskell.nix Project

Sometimes you will need some extra tools to build your project. For the RecordDotSyntax feature, you will need a ghc plugin or a pre processer to build.

This flag is used by cabal, but looks like cabal only builds the library but won’t add the executable into the PATH during the following build process. There is a issue to track this: https://github.com/haskell/cabal/issues/8434

There also is a issue track in haskell.nix: https://github.com/input-output-hk/haskell.nix/issues/839