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

[Alexander Yermolovich via llvm-commits]

ayermolo wrote:

> > Can Lazy argument be removed from &getDWOUnits(bool Lazy), since we always now pass false to underlying call.
> 
> We don't always pass false. Only in the threadsafe code do we pass false. In the single threaded code we still pass true for Lazy since it is ok.

ah right it's a virtual function. Nevermind.

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