[llvm] Make DWARFUnitVector threadsafe. (PR #71487)

[David Blaikie via llvm-commits]

https://github.com/dwblaikie approved this pull request.

Sounds OK to me.

Bonus points if you added test coverage for this - though I guess the multithreaded path isn't tested in llvm-dwarfdump? (we could add a not-intended-for-consumers flag that enables multithreaded mode, but with a single thread (or, heck, maybe with multiple threads for parsing or something) - then you could demonstrate that the non-lazy functionality is used by inserting some invalid DWARF and showing that in multithreaded mode it hits a failure due to non-laziness, but it isn't hit in single threaded mode) - Though perhaps the laziness is only accessible through llvm-symbolizer, not llvm-dwarfdump, so the multithreading would have to be there.

https://github.com/llvm/llvm-project/pull/71487