[clang] [llvm] [offload][OpenMP] Improve cross-team reduction grid selection (PR #208253)

[Robert Imschweiler via cfe-commits]

ro-i wrote:

> Can you add a test?

yeah, this should now be possible without depending on specific hardware. I initially had no test because I was following a different selection strategy, but with the current redistribution, it's not a problem anymore. Thanks for the reminder!

https://github.com/llvm/llvm-project/pull/208253