[20.03] haskellPackages.ghcide: Fix build

[maralorn]

Motivation for this change

ghcide is marked as broken and is not building. With these changes it builds.

Please let me know if I should structure the overrides in a different way.
When this PR is approved I will port it to the haskell-updates branch. But first I wanna know if I did this right.
I am especially confused by the recursive library overrides. It‘s not pretty this way. e.g. the override for regex-tdfa_1_3_1_0 which needs a pinned regex-base version is now twice in the file.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

[cdepillabout]

@maralorn Thanks for working on this. I think a lot of Haskellers have been trying out ghcide. It'd be nice if people could just get it from nixpkgs.

[maralorn]

@cdepillabout I do believe I have now fixed all your concerns and all my concerns.

• Moved the lsp stuff to hackage-packages and put that in the yaml, so that it doesn‘t get lost.
• Activated hydra builds.
• figured out the use of self, so that I need to do less overrides on my own.

[cdepillabout]

@maralorn

One more change and this can be merged in:

haddock-library_1_8_0 needs to have the hydraPlatforms = stdenv.lib.platforms.none line removed.

Once that is done, I will merge this in. I have confirmed that ghcide was able to build.