Enable parallel builds

[samisagit]

https://www.reddit.com/r/haskell/comments/bd1tfb/why_isnt_ghc_multithreaded/?utm_medium=android_app&utm_source=share

Seems to imply build times would reduce, and if tests are marked as parallel safe (spec below) we might save a bunch of time once there are a few systests

https://hspec.github.io/parallel-spec-execution.html