[llvm] [llvm-dwp] Replace MCStreamer with direct ELF writer for zero-copy output (PR #192112)

[Farid Zakaria via llvm-commits]

fzakaria wrote:

I see. @dwblaikie how about starting here and refining.
I was able to consolidate ~200 lines of code; perhaps we can do more follow-up in subsequent PRs.
Our team always prefer to land upstream first so let me know what everyone decides.

Here are some stats as to why I am interested in seeing this optimization:
P90 for llvm-dwp is >4.5 minutes
p99+ for llvm-dwp is >8 minutes

Getting that down would be a big win I think.

https://github.com/llvm/llvm-project/pull/192112