[openmp] [llvm] [mlir] [clang] [OpenMP] Introduce the KernelLaunchEnvironment as implicit argument (PR #70401)

[via cfe-commits]

ronlieb wrote:

> performance degradation observed for this patch on trunk build : hpc2021 8 mpi210's reference run 518.tealeaf 10.8% 534.hpgmg 7.3%

both of these benchmarks which exhibited performance regressions, contain reductions.

https://github.com/llvm/llvm-project/pull/70401