The GHC-side getNameToInstancesIndex filters out incorrectly some
instances because it is not aware of what modules are visible. Using
runTcInteractive means that ie_visible gets initialized to a one
module set containing some dummy GHCi module. This is clearly not the
module set we want to check against to see if a given orphan instance
is visible or not.
In fact, GHC has no way of knowing what we want that module set to be
since it doesn't know ahead of time which modules Haddock is making its
docs for. The fix is just to pass that set in as an argument.