[clang] [Clang][HIP][CUDA] Add `__cluster_dims__` and `__no_cluster__` attribute (PR #156686)

[Erich Keane via cfe-commits]

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@@ -1557,6 +1557,23 @@ def HIPManaged : InheritableAttr {
   let Documentation = [HIPManagedAttrDocs];
 }
 
+def CUDAClusterDims : InheritableAttr {
+  let Spellings = [GNU<"cluster_dims">, Declspec<"__cluster_dims__">];
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erichkeane wrote:

these spellings don't look right to me.  Which spellings are you trying to enable?  Also, don't use the `__` before/after in the spellings, we should add that automatically.

https://github.com/llvm/llvm-project/pull/156686