[llvm] [BOLT][NFC] Unify two symbol table iterations (PR #90724)

[Amir Ayupov via llvm-commits]

aaupov wrote:

> https://github.com/llvm/llvm-project/blob/main/bolt/docs/OptimizingClang.md
> 
> Is this still recommened setup?

The guide covers more than what we need in this case. You can just run on BOLT on any Clang binary, for instance, you can try BOLT instrumentation:
```
llvm-bolt clang-18 -instrument -o clang-18.bolt.inst
```

https://github.com/llvm/llvm-project/pull/90724