[clang] [CIR][AMDGPU] Implement the clang::atomic statement attribute (PR #225364)

[via cfe-commits]

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@@ -21,6 +21,84 @@ using namespace clang;
 using namespace clang::CIRGen;
 using namespace cir;
 
+/// Map a constant integeral to memory order.
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skc7 wrote:

```suggestion
/// Map a constant integral to memory order.
```

https://github.com/llvm/llvm-project/pull/225364