[clang] [Clang] disallow attributes on void parameters (PR #124920)

[Aaron Ballman via cfe-commits]

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@@ -53,3 +53,14 @@ alignas(4) auto PR19252 = 0;
 
 // Check the diagnostic message
 class alignas(void) AlignasVoid {}; // expected-error {{invalid application of 'alignas' to an incomplete type 'void'}}
+
+namespace GH108819 {
+void a([[maybe_unused]] void) {}                 // expected-warning {{attribute 'maybe_unused' cannot be applied to a 'void' parameter}}\
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AaronBallman wrote:

Shafik's availability may be odd this week because of WG21 meetings in Hagenberg. The new test cases look good to me, so I think you're fine to land the PR and we can address any additional test coverage needs post-commit if Shafik has other cases in mind.

https://github.com/llvm/llvm-project/pull/124920