patch GHC

[chris-martin]

@stackptr Applied the patch you mentioned in Slack, please try it out!

(I'm still waiting for mine to build locally)

From:

• https://discourse.nixos.org/t/patching-ghc-for-your-project/9614/7
• https://github.com/input-output-hk/haskell.nix/blob/master/overlays/patches/ghc/sanity-check-find-file-name.patch