[clang] [HLSL] Run availability diagnostic on exported functions (PR #97352)

[Helena Kotas via cfe-commits]

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@@ -129,6 +129,55 @@ class MyClass
   }
 };
 
+// Exported function without body - not used
+export void exportedFunctionUnused(float f);
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hekota wrote:

Also adding test for this here: https://github.com/llvm/llvm-project/pull/97370

https://github.com/llvm/llvm-project/pull/97352