[llvm] `dwarf2yaml.cpp` optimizations (PR #179048)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

In principle, this looks reasonable to me. That being said, do you have any performance figures to back this up or is this fixing some other issue, like a clang-tidy check etc?

In other words, what's the motivation for changing the code?

https://github.com/llvm/llvm-project/pull/179048