[llvm] [mlir] [OpenMP][OMPIRBuilder] Fix lastiter assertion in target workshare loop (PR #214996)

[Abid Qadeer via llvm-commits]

https://github.com/abidh requested changes to this pull request.

This does not compile. When I fixed the build, it is failing its own and 2 existing tests. My main concern is with the approach. lastiter is only consumed by the linear finalization in convertOmpWsloop, but this makes every target loop pay for it. Could we emit it only when it is needed

https://github.com/llvm/llvm-project/pull/214996