[clang-tools-extra] [clang-tidy] introduce a unused local non trival variable check (PR #76101)

[Tyler Rockwood via cfe-commits]

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+.. title:: clang-tidy - bugprone-unused-local-non-trivial-variable
+
+bugprone-unused-local-non-trivial-variable
+==========================================
+
+Warns when a local non trivial variable is unused within a function.
+
+In the following example, `future2` would generate a warning that it is unused.
+
+.. code-block:: c++
+
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rockwotj wrote:

Took a shot at this. PTAL.

https://github.com/llvm/llvm-project/pull/76101