[llvm] Add initial support for SPE brstack format (PR #129231)

[Paschalis Mpeis via llvm-commits]

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@@ -1527,9 +1551,11 @@ void DataAggregator::printBranchStacksDiagnostics(
 }
 
 std::error_code DataAggregator::parseBranchEvents() {
-  outs() << "PERF2BOLT: parse branch events...\n";
-  NamedRegionTimer T("parseBranch", "Parsing branch events", TimerGroupName,
-                     TimerGroupDesc, opts::TimeAggregator);
+  std::string BranchEventTypeStr =
+      !opts::ArmSPE ? "branch events" : "SPE branch events in LBR-format";
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paschalis-mpeis wrote:

nit:

```suggestion
  std::string BranchEventTypeStr =
      opts::ArmSPE ? "SPE branch events" : "branch events";
```

https://github.com/llvm/llvm-project/pull/129231