Closes #544. It looks like when we call 'showSDocUnsafe' it uses `unsafeGlobalDynFlags` wwhich the `settings` field is not initialised unless someone calls `setUnsafeGlobalDynFlags`, `initGhcMonad` or `runGhc` and throws a panic. I couldn't pinpoint the exact cause, but I suspect probably there was a change either on Ormolu or ghc-lib-parser which removed a call to one of the functions above before we print manualExts. Anyway, we actually don't need to call `showSDocUnsafe` since we already have a populated `DynFlags`. This commit removes the unsafe call and passes the `DynFlags` we have to `showSDoc`.