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

[Akash Banerjee via llvm-commits]

TIFitis wrote:

> Not super familiar with the work here, but could we maybe split it as - one patch for OpenMPIRBuilder changes with tests in OpenMPIRBuilderTest.cpp and then second patch for the clang changes to use those OpenMPIRBuilder changes? Would the CI tests cause issues?

Only the functions required for OpenMP reductions directive are being moved in this patch and the OpenMPIRBuilder changes are only to facilitate this move.

No new functionality is being added.

If we were to move only a subset of the functions then we would have to add extra code to remove the dependancy on Clang CGF etc which is unnecessary.

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