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

[Greg Clayton via llvm-commits]

https://github.com/clayborg requested changes to this pull request.

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.

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