[clang] [openmp] [OpenMP 6.0 ]Codegen for Reduction over private variables with reduction clause (PR #134709)

[CHANDRA GHALE via cfe-commits]

chandraghale wrote:

@alexey-bataev Added few more changes on top, to be on accordance with spec.  Shared copy is updated with values from private copies until all updates are complete, before combining into the original list item. Hope the changes are fine with you.

https://github.com/llvm/llvm-project/pull/134709