[clang-tools-extra] [clang-tidy] Store stateless check factories as function pointers (PR #202625)

[via cfe-commits]

github-actions[bot] wrote:

<!--LLVM CODE LINT COMMENT: clang-tidy-->


:warning: C/C++ code linter, clang-tidy found issues in your code. :warning:

<details>
<summary>
You can test this locally with the following command:
</summary>

```bash

git diff -U0 origin/main...HEAD -- clang-tools-extra/clang-tidy/ClangTidyModule.cpp clang-tools-extra/clang-tidy/ClangTidyModule.h |
python3 clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py   -path build -p1 -quiet
```

</details>

<details>
<summary>
View the output from clang-tidy here.
</summary>

```
clang-tools-extra/clang-tidy/ClangTidyModule.h:101:2: warning: preprocessor condition can be written more concisely using '#ifdef' [readability-use-concise-preprocessor-directives]
  101 | #if defined(__clang__)
      |  ^~~~~~~~~~~~~~~~~~~~~
      |  ifdef __clang__
```

</details>


https://github.com/llvm/llvm-project/pull/202625