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

[Jonas Devlieghere via llvm-commits]

JDevlieghere wrote:

> DWARFLinker would still need to be deterministic, even on old/bad/different input 

+1

> though maybe Apple & other folks would be open to it having an error on "bad" input rather than having to figure out a way to have a deterministic successful output.

As long as the input DWARF is valid, we need to be able to link it. Maybe a slow path would be okay if we can guarantee our toolchain doesn't trigger it (i.e. clang & Swift). 

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