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

[Alexey Bataev via cfe-commits]

alexey-bataev wrote:

> I haven't removed any code logic or made alterations that would affect these AFAIK. I'm not sure however if these were supported in the first place. If @alexey-bataev has any tests for them then I could try them out before and after the patch and post an update here.

I don't remember exactly the test (added them more than 5 years ago), but both UDR and non-trivial constructors should be supported. I just remember that there were some limitations for UDR for NVPTX, like trivial UDR operations to use NVPTX fast builtins. 

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