[llvm] Make llvm::telemetry::Manager::preDispatch protected. (PR #127114)

[Pavel Labath via llvm-commits]

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@@ -150,6 +146,11 @@ class Manager {
   // Register a Destination.
   void addDestination(std::unique_ptr<Destination> Destination);
 
+protected:
+  // Optional callback for subclasses to perform additional tasks before
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labath wrote:

It shouldn't really be empty, it should return `Error::success()` (that's what I tried to indicate with "doing nothing, successfully", sorry if I wasn't clear)

https://github.com/llvm/llvm-project/pull/127114