[clang] [llvm] [openmp] [Clang][OpenMP] Add `#pragma omp flatten` loop directive + `depth` clause (PR #206977)

[Michael Kruse via llvm-commits]

================
@@ -0,0 +1,12 @@
+// RUN: c-index-test -test-load-source local %s -fopenmp=libomp -fopenmp-version=60 | FileCheck %s
----------------
Meinersbur wrote:

```suggestion
// RUN: c-index-test -test-load-source local %s -fopenmp=libomp -fopenmp-version=61 | FileCheck %s
```
flatten is a OpenMP 6.1 feature

OMP.td does allow the specifying the version of directive (yet), but the tests themselves should test the version it was introduced

https://github.com/llvm/llvm-project/pull/206977