[clang] Reapply "[clang analysis][thread-safety] Handle return-by-reference..… (PR #68572)

[Arthur Eubanks via cfe-commits]

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@@ -1061,18 +1061,20 @@ def Most : DiagGroup<"most", [
  ]>;
 
 // Thread Safety warnings
-def ThreadSafetyAttributes : DiagGroup<"thread-safety-attributes">;
-def ThreadSafetyAnalysis   : DiagGroup<"thread-safety-analysis">;
-def ThreadSafetyPrecise    : DiagGroup<"thread-safety-precise">;
-def ThreadSafetyReference  : DiagGroup<"thread-safety-reference">;
-def ThreadSafetyNegative   : DiagGroup<"thread-safety-negative">;
+def ThreadSafetyAttributes       : DiagGroup<"thread-safety-attributes">;
+def ThreadSafetyAnalysis         : DiagGroup<"thread-safety-analysis">;
+def ThreadSafetyPrecise          : DiagGroup<"thread-safety-precise">;
+def ThreadSafetyReference        : DiagGroup<"thread-safety-reference">;
+def ThreadSafetyReferenceReturn  : DiagGroup<"thread-safety-reference-return">;
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aeubanks wrote:

it's fine to put this in `ThreadSafety` and have it on by default (which it should be because it's improving thread safety analysis) since now people can turn it off with `-Wno-thread-safety-reference` while cleaning up their codebase

https://github.com/llvm/llvm-project/pull/68572