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

[Jonas Devlieghere via llvm-commits]

JDevlieghere wrote:

Why is the debug info section so much smaller when using the parallel linker? Is it really that much more efficient than the Apple one, and if so, where are the gains coming from? Are we eliminating types that the dsymutil isn't, like base types? I'm a little skeptical, but I can also imagine the new approach is a lot better because it doesn't need to keep things like forward declarations until it sees a definition, etc. 

> Note: Sometimes DWARFLinkerParallel may produce non-deterministic results.

I know you're aware but I'll emphasize again that that's a non-starter for us. It sounds like you have patches in the works so that's great!

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