First, we improve some of the rules around -I include dirs, and CPP opts. Then, we just specify the RTS's include dirs normally (locally per the package and in the package conf), and then everything should work normally. The primops.txt.pp rule needs no extra include dirs at all, as it no longer bakes in a target platfom. Reverts some of the extra stage arguments I added in 05419e55, as they are no longer needed.
Code owners : Ben Gamari