[clang] [C23][Parser] Diagnostic for attribute declaration where statement is required (PR #146224)

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@@ -80,6 +81,11 @@ Parser::ParseStatementOrDeclaration(StmtVector &Stmts,
   assert((CXX11Attrs.empty() || Res.isInvalid() || Res.isUsable()) &&
          "attributes on empty statement");
 
+  if (HasStdAttr && getLangOpts().C99 &&
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yronglin wrote:

I originally want to emit this warning in C99 mode, but now I have changed the condition here to C23.

https://github.com/llvm/llvm-project/pull/146224