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

[Matthew Nagy via cfe-commits]

================
@@ -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">;
----------------
gbMattN wrote:

Perhaps this could be renamed to be more descriptive?
Address sanitizer on line 1599 has
```
// AddressSanitizer frontend instrumentation remarks.
def SanitizeAddressRemarks : DiagGroup<"sanitize-address">;
```

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