[clang] [Clang] Warn when `std::atomic_thread_fence` is used with `fsanitize=thread` (PR #166542)

[Matthew Nagy via cfe-commits]

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@@ -1769,3 +1769,5 @@ def ExplicitSpecializationStorageClass : DiagGroup<"explicit-specialization-stor
 
 // A warning for options that enable a feature that is not yet complete
 def ExperimentalOption : DiagGroup<"experimental-option">;
+
+def TSan : DiagGroup<"tsan">;
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gbMattN wrote:

Hmm, unless you can think of any reason not to, I think copying the ASan style exactly, and maybe moving your change to be next to it to logically group them together would be better

https://github.com/llvm/llvm-project/pull/166542