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

[Aaron Ballman via cfe-commits]

================
@@ -15,18 +15,19 @@ void f(int n) {
       return;
     }
   case 2:
+    // FIXME: Should we emit an error {{fallthrough annotation does not directly precede switch label}}?
----------------
AaronBallman wrote:

Yeah that seems like a regression in behavior.

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