Initialize GHC plugins
Initialize GHC plugins

Since GHC-8.6 plugins need to be initialized on a per module basis.
Without this any modules using plugins fail to compile inside doctest.

This code is adapted from how this was fixed in haddock:
https://github.com/haskell/haddock/pull/983/files#diff-a6119dd2da927bbff2c39eda86cdc733

sol/doctest,sol/doctest