swift234

DeadObjectElemination: fix two problems with handling of the tuple_extract following an array init call

1) handle cases where the tuple_extract is not in the same basic block as the init call. This is not a correctness issue, but might miss some opportunities.
2) bail if there are multiple tuple_extract. This is a correctness issue, but a theoretical one. I don't think that in reality we will ever get multiple tuple_extracts out of SILGen.