[clang-tools-extra] [clang-tidy] Implement alphabetical order test (PR #166072)

[Baranov Victor via cfe-commits]

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+// RUN: %python %S/../../../clang-tidy/tool/clang-tidy-alphabetical-order-check.py -o %t.clang-tidy-checks-list.rst
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vbvictor wrote:

Why should it be in CMake, could you elaborate?
We already have similar tests, like this https://github.com/llvm/llvm-project/blob/main/clang/test/Format/docs_updated.test to ensure that docs are updated.
What would be the workflow involving Cmake?

https://github.com/llvm/llvm-project/pull/166072