[OpenMPOpt] Move dedup runtime calls after init for target regions

Deduplication in OpenMPOpt finds redundant OpenMP runtime calls and replaces them with a single call placed in the earliest safe location in the IR. When deduplication happens in a target region this patch makes sure replacement calls are put after target_init.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D106556