[clang] [llvm] [mlir] [OpenMP] Migrate GPU Reductions CodeGen from Clang to OMPIRBuilder (PR #80343)

[Johannes Doerfert via cfe-commits]

https://github.com/jdoerfert commented:

Some comments inlined.

Do we support non trivial constructors for reduction variables?
Similarly, did we support user defined reductions?
If either questions is answered with yes, do we keep that support?

We might need to ask Alexey.


https://github.com/llvm/llvm-project/pull/80343