[clang-tools-extra] [clang-tidy] Add llvm-regex check (PR #207407)

[via cfe-commits]

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+.. title:: clang-tidy - llvm-regex
+
+llvm-regex
+==========
+
+The checker detects malformed regex patterns defined in a single string literal
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EugeneZelenko wrote:

```suggestion
Detects malformed regex patterns defined in a single string literal
```

https://github.com/llvm/llvm-project/pull/207407