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

[Farid Zakaria via llvm-commits]

fzakaria wrote:

@jh7370 it is not easy or straightforward to merge more due to some assumptions MCStreamer makes; or at least not to me.

Whether this simpler ELF writer utility I had extracted out can be re-leveraged in other tools like ObjCopy is I think something to investigate but I think also outside the bounds of this PR?

Anyways; I might propose the patch internally as is unless there is other big concerns. The speedups seem very appealing.

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