[clang] [AArch64][SME] Add diagnostics to CheckConstexprFunctionDefinition (PR #121777)

[Kerry McLaughlin via cfe-commits]

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@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-gnu -std=c++23 -fsyntax-only -verify %s
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kmclaughlin-arm wrote:

I think adding attributes to lambdas before the parameter list was only allowed in C++23. If I don't pass this flag, the error emitted is instead `"'attribute' in this position is a C++23 extension"`.

https://github.com/llvm/llvm-project/pull/121777