[llvm] [Support] Fix memory leak in `Timer.cpp` on shutdown (PR #159983)

[Fangrui Song via llvm-commits]

================
@@ -305,14 +306,24 @@ TimerGroup::~TimerGroup() {
     PrintQueuedTimers(*OutStream);
   }
 
+  auto unlink = [&]() {
+    *Prev = Next;
+    if (Next)
+      Next->Prev = Prev;
+  };
+
+  // If the managed instance is already dead, it means we're in the CRT
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MaskRay wrote:

I am confused by this comment.

`llvm::TimerGroup::acquireTimerGlobals()` frees ManagedStatic. Is the leak due to timerLock() re-constructing the ManagedStatic?

https://github.com/llvm/llvm-project/pull/159983