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

[James Henderson via llvm-commits]

jh7370 wrote:

> @jh7370 @dwblaikie should I remove the top commit then and go back to the original? Another option is to keep the micro-library but just not integrated with ELFObjectWriter.

I skimmed the original version and it looks okay as a shorter term option, if @dwblaikie is in agreement.

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