[SCEV] PtrToInt on non-integral pointers is allowed

As per (committed without review) @reames's rGac81cb7e6dde9b0890ee1780eae94ab96743569b change,
we are now allowed to produce `ptrtoint` for non-integral pointers.
This will unblock further unbreaking of SCEV regarding int-vs-pointer type confusion.

Reviewed By: mkazantsev

Differential Revision: https://reviews.llvm.org/D104322