This should help guard against unwanted updates.
Fixes ghcjs 8.6.5 and 8.8.4. Uses emscripten for ghcjs 8.8 and adds scripts for building ghcjs 8.8. Many fixes for ghcjs test failures. Includes relocatableConfigFiles for making relocatable ghcjs bundles.
Adds `ghcjs` to haskell.nix Co-authored-by: Hamish Mackenzie <Hamish.K.Mackenzie@googlemail.com> Co-authored-by: Michael Bishop <cleverca22@gmail.com>