[flang] [llvm] [mlir] [flang][MLIR][OpenMP] make reduction by-ref toggled per variable (PR #92244)

[Kiran Chandramohan via llvm-commits]

https://github.com/kiranchandramohan commented:

Looks mostly OK to me. Have some minor comments inline.

Would adding the `byref` attribute to the Reduction Declaration Operation work?

https://github.com/llvm/llvm-project/pull/92244