[clang] [Clang][AArch64] Change SME attributes for shared/new/preserved state. (PR #76971)

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@@ -255,6 +255,22 @@ class AttributeCommonInfo {
     return SpellingIndex != SpellingNotCalculated;
   }
 };
+
+enum class KeywordAttributeParseArgumentsKind { None, Optional, Required };
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rsandifo-arm wrote:

I think this must fundamentally be a boolean required/none choice.  The point is that a `(` that follows the keyword must either always be part of the attribute or always part of the containing declaration.  It isn't something that can/should be inferred from context.

https://github.com/llvm/llvm-project/pull/76971