[llvm] Default to LLDB debugger tuning for shared library builds (PR #83083)

[Alexander Richardson via llvm-commits]

arichardson wrote:

> & sounded like the plan from the last review was to add a warning to the pretty printer - rather than to do this?

I was planning to also do that, just haven't got around to that part yet.

Regarding this change, how would you feel about an opt-in CMake option that adds this flag when enabled? I've had lots of cases where messing with `CMAKE_C(XX)_FLAGS` resulted in weird failures, so I'd prefer a boolean flag that just calls add_compile_options().

https://github.com/llvm/llvm-project/pull/83083