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

[Michael Kruse via llvm-commits]

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@@ -0,0 +1,25 @@
+// C++20 module interface with `#pragma omp flatten` — emit BMI + import; AST retains directive.
+//
+// RUN: rm -rf %t && split-file %s %t && cd %t
+// RUN: %clang_cc1 -std=c++20 -fopenmp -fopenmp-version=60 -triple x86_64-unknown-linux-gnu %t/FlattenMod.cppm -emit-module-interface -o %t/FlattenMod.pcm
+// RUN: %clang_cc1 -std=c++20 -fopenmp -fopenmp-version=60 -triple x86_64-unknown-linux-gnu %t/UseFlattenMod.cpp -fmodule-file=FlattenMod=%t/FlattenMod.pcm -ast-dump-all | FileCheck %t/FlattenMod.cppm
----------------
Meinersbur wrote:

```suggestion
// RUN: %clang_cc1 -std=c++20 -fopenmp -fopenmp-version=61 -triple x86_64-unknown-linux-gnu %t/FlattenMod.cppm -emit-module-interface -o %t/FlattenMod.pcm
// RUN: %clang_cc1 -std=c++20 -fopenmp -fopenmp-version=61 -triple x86_64-unknown-linux-gnu %t/UseFlattenMod.cpp -fmodule-file=FlattenMod=%t/FlattenMod.pcm -ast-dump-all | FileCheck %t/FlattenMod.cppm
```

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