[ObjCARC] Handle ARCInstKind::ClaimRV in OptimizeIndividualCalls.

When support for objc_unsafeClaimAutoreleasedReturnValue has been added to the
ARC optimizer in r258970, one case was missed which would lead the optimizer
to execute an llvm_unreachable. In this case, just handle ClaimRV in the same
way we handle RetainRV.

llvm-svn: 261134