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

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@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c2x -verify %s
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yronglin wrote:

c2x-fallthrough2.c was reverted, we don't need it in current implementation, but I change c2x to c23 in c2x-fallthrough.c

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