[flang][OpenMP] Guard lastprivate scoping on DO (#157760)
Add HLFIR FileCheck ensuring `lastprivate(v)` on an `omp do` is realized
as privatization on the inner wsloop and not on the enclosing `omp
parallel`.
This matches OpenMP semantics and prevents regressions.
- No `private(v)` at `omp.parallel`
- `omp.wsloop ... private(...)` present
Unable to reproduce #157035 on current main; this test documents the
expected lowering.
p.s- do refer to
[delayed-privatization](https://lists.llvm.org/pipermail/mlir-commits/2025-January/088206.html?utm_source=chatgpt.com)
<img width="2940" height="1912" alt="image"
src="https://github.com/user-attachments/assets/5c3a0656-fe0a-4bd5-be98-b626a7a719c1"
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