[clang] [clang] Improve `_Alignas` on a `struct` declaration diagnostic (PR #65638)

[Erich Keane via cfe-commits]

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@@ -186,14 +186,14 @@ class AttributeCommonInfo {
   bool isGNUScope() const;
   bool isClangScope() const;
 
-  bool isCXX11Attribute() const { return SyntaxUsed == AS_CXX11 || IsAlignas; }
-
+  bool isAlignas() const { return IsAlignas; }
+  bool isCXX11Attribute() const { return SyntaxUsed == AS_CXX11; }
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erichkeane wrote:

I can see this both ways. It is typically used AFAIK as a 'is this a C++ spelling' despite not exactly meaning that.  On the other hand, as Aaron mentions, this is changing its meaning fairly significantly.  I'm still on the fence here.

https://github.com/llvm/llvm-project/pull/65638