[LoopLoadElim] Filter away candidates that stop being AddRecs after loop versioning. PR47457

The test in PR47457 demonstrates a situation when candidate load's pointer's SCEV
is no loger a SCEVAddRec after loop versioning. The code there assumes that it is
always a SCEVAddRec and crashes otherwise.

This patch makes sure that we do not consider candidates for which this requirement
is broken after the versioning.

Differential Revision: https://reviews.llvm.org/D87355
Reviewed By: asbirlea