[lldb] [llvm] DEBUGINFOD based DWP acquisition for LLDB (PR #70996)

[Kevin Frei via llvm-commits]

kevinfrei wrote:

> We need to respect the setting `symbols.enable-external-lookup` and not do anything with debuginfod if this is set to false.
> 
> You can get this value by calling:
> 
> ```
> ModuleList::GetGlobalModuleListProperties().GetEnableExternalLookup()
> ```
> 
> Otherwise I fear that the linux buildbots will start failing if we get extra system library symbols if debuginfod is enabled via the environment variable.

Fixed that up, rebased and push -f 'ed

https://github.com/llvm/llvm-project/pull/70996