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

[Michael Kruse via cfe-commits]

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@@ -0,0 +1,143 @@
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -std=c++20 -fopenmp -fopenmp-version=61 -fsyntax-only -Wall -Wuninitialized -verify=expected,omp61 %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -std=c++20 -fopenmp -fopenmp-version=60 -fsyntax-only -Wall -Wuninitialized -verify=expected %s
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Meinersbur wrote:

```suggestion
```
flatten is not valid OpenMP 6.0.

I hope we eventually get an infrastructure to reject directives based on the OpenMP version, not just clauses

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