[clang] [Clang] Enable -Wunused-template under -Wall (PR #206123)

[Aaron Ballman via cfe-commits]

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@@ -679,6 +676,10 @@ Improvements to Clang's diagnostics
 - Diagnostics for the C++11 range-based for statement now report the correct
   iterator type in notes for invalid iterator types.
 
+- ``-Wunused-template`` is now part of ``-Wall``. It diagnoses unused function
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AaronBallman wrote:

```suggestion
- ``-Wunused-template`` is now part of ``-Wunused`` (which is enabled by ``-Wall``). It diagnoses unused function
```

https://github.com/llvm/llvm-project/pull/206123