[llvm] [DebugInfo/DWARF] Fix data race in DWARFUnit DIE extraction (PR #180470)

[David Blaikie via llvm-commits]

dwblaikie wrote:

(at this point - if someone wants to do a perf analysis (like how long does llvm-dwarfdump on a large binary take (maybe with a profile) with multithreading enabled or disabled - if multithreading enabled doesn't show up in a profile... maybe we should just accept that complexity as being a core feature of the API without trying to stuff it into one particular area/keep it out of other areas)

https://github.com/llvm/llvm-project/pull/180470