[llvm] [GitHub] Bump clang-tidy version to 21th and add sccache in CI (PR #160551)

[Baranov Victor via llvm-commits]

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@@ -59,6 +60,13 @@ jobs:
 
       - name: Install Python dependencies
         run: python3 -m pip install -r llvm/utils/git/requirements_linting.txt
+
+      - name: Setup ccache
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vbvictor wrote:

One problem I faced with `sccache` is that it doesn't store/restore results when I run multiple the job multiple times [here](https://github.com/llvm/llvm-project/pull/160193).
The warnings are:
`Warning: Cache not found for keys: sccache-premerge-clang-tidy-`
`Warning: Saving cache failed: Error: Path Validation Error: Path(s) specified in the action for caching do(es) not exist, hence no cache is being saved.`

I suspect I need to create this key in somewhere or it will start to work after PR is merged into main?

I can see in other workflows similar setup of `sccache`, 
https://github.com/llvm/llvm-project/blob/4d4cb757f94470b95458fcbe3b88332b212feeee/.github/workflows/ci-post-commit-analyzer.yml#L46-L59

Apart from this problem, shall I create a dedicated key for "clang-tidy" runs or reuse some existing one? In theory this `ccache` should store a little data because all it only compile codegen targets.

https://github.com/llvm/llvm-project/pull/160551