[llvm] [DWARFLinkerParallel] Add support for -odr mode. (PR #68721)

[via llvm-commits]

avl-llvm wrote:

> Did we come up with a solution for determinism that doesn't depend on the generator? My understanding was that we're okay with taking a penalty in terms of performance, but does the code reflect this, or will the current version of this patch still generate non-deterministic results with other producers or older version of clang that don't have Michael's changes?

This version of patch will produce non-deterministic results if input have non-consistent DWARF(these are old-producers and current clang(even with Michael's patch)). I proposed to implement full-deterministic version as a follow-up patch. Current patch is already huge and it would be good to reduce it's size. I suggest following order of patches:

1. this patch.
2. patch refactoring directory structure. So that DWARFLinker directory contains code for common library, Apple linker, LLVM linker.
3. add --deterministic cl option.
4. implement full deterministic mode which will produce deterministic output for current clang and old-producers.

What do you think?

https://github.com/llvm/llvm-project/pull/68721