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

[Zeyi Xu via cfe-commits]

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@@ -0,0 +1,140 @@
+// RUN: %check_clang_tidy -std=c++17 %s llvm-regex %t
+
+namespace std {
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zeyi2 wrote:

I think you can directly use `#include <string>` instead of manual mocking.

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