Draft: rts: Make LOOKS_LIKE_INFO_PTR a bit more strict
In particular, we now verify that the info table doesn't reside in the dynamic heap.
Test Plan: Validate
Reviewers: simonmar, osa1
Reviewed By: osa1
Subscribers: rwbarton, thomie, carter
Differential Revision: https://phabricator.haskell.org/D4759
Edited by Ben Gamari