[llvm] [llvm-exegesis] Add support for pinning benchmarking process to a CPU (PR #85168)

[Clement Courbet via llvm-commits]

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@@ -310,6 +321,29 @@ class SubProcessFunctionExecutorImpl
     }
 
     if (ParentOrChildPID == 0) {
+      if (BenchmarkProcessCPU) {
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legrosbuffle wrote:

[nit] `BenchmarkProcessCPU.has_value()`

https://github.com/llvm/llvm-project/pull/85168