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

[Farid Zakaria via llvm-commits]

fzakaria wrote:

@dwblaikie I factored out a small ELF writer. I didn't see any other integrations with MCStreamer that made sense.
Let me know what you think.

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