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

[Michael Kruse via cfe-commits]

================
@@ -0,0 +1,102 @@
+// Check code generation
+// RUN: %clang_cc1 -verify -triple x86_64-pc-linux-gnu -std=c++20 -fopenmp -fopenmp-version=60 -emit-llvm %s -o - | FileCheck %s
----------------
Meinersbur wrote:

```suggestion
// RUN: %clang_cc1 -verify -triple x86_64-pc-linux-gnu -std=c++20 -fopenmp -fopenmp-version=61 -emit-llvm %s -o - | FileCheck %s
```

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