[clang] [clang] Improve diagnostic on [[nodiscard]] attribute (PR #112521)

[via cfe-commits]

================
@@ -416,6 +416,9 @@ Improvements to Clang's diagnostics
   name was a reserved name, which we improperly allowed to suppress the
   diagnostic.
 
+- Clang now includes the return type of the function or constructor in the warning generated
+  when `[[nodiscard]]` is triggered by its placement on return types instead of function itself.
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Sirraide wrote:

```suggestion
- When diagnosing an unused return value of a type declared ``[[nodiscard]]``, the type
  itself is now included in the diagnostic.
```
I think this way it’s a bit easier to understand what’s happening here. This is the best I could do while trying to avoid the mouthful that is ‘ignoring a value returned from a call to a function returning a type marked nodiscard’.

https://github.com/llvm/llvm-project/pull/112521