[clang] [clang][timers][modules] Fix a timer being started when it's running (PR #154231)

[Alexander Kornienko via cfe-commits]

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@@ -11003,7 +11003,8 @@ void ASTReader::diagnoseOdrViolations() {
 }
 
 void ASTReader::StartedDeserializing() {
-  if (++NumCurrentElementsDeserializing == 1 && ReadTimer.get())
+  if (llvm::Timer *T = ReadTimer.get();
+      ++NumCurrentElementsDeserializing == 1 && T && !T->isRunning())
     ReadTimer->startTimer();
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alexfh wrote:

nit: This can now refer to T instead of ReadTimer as well.

https://github.com/llvm/llvm-project/pull/154231