[llvm] [llvm-exegesis] Add thread IDs to subprocess memory names (PR #84451)

[Florian Hahn via llvm-commits]

fhahn wrote:

It looks like this breaks building at least on macOS, so I went ahead and revert the change for now in aefad27096bba513f06162fac2763089578f3de4

This is the error I am seeing:
```
llvm/tools/llvm-exegesis/lib/SubprocessMemory.cpp:146:33: error: out-of-line definition of 'setupAuxiliaryMemoryInSubprocess' does not match any declaration in 'llvm::exegesis::SubprocessMemory'
Expected<int> SubprocessMemory::setupAuxiliaryMemoryInSubprocess(
```

https://github.com/llvm/llvm-project/pull/84451