This commit adds handling for a corner case of
MergePointeesOfPointerUnion, that wasn't handled before.
Said corner case happens when one of the scalars that gets merged as
part of the DLAStep operations is also itself a pointer to another
scalar that gets merged.
This wasn't accounted for before this commit, but it's actually a valid
scenario that can happen on some inputs.
Pietro Fezzardi
ff747c069d