[SimplifyCFG] Don't sink loads/stores with swifterror pointers.

swifterror pointers can only be used as pointer operands of load & store
instructions (and as swifterror argument of a call). Sinking loads or
stores with swifterror pointer operands would require introducing a
select of of the pointer operands, which isn't allowed.

Check for this condition in canSinkInstructions.

Reviewed By: aschwaighofer

Differential Revision: https://reviews.llvm.org/D158083