[llvm] [llvm][amdgpu] Handle indirect refs to LDS GVs during LDS lowering (PR #124089)

[Kareem Ergawy via llvm-commits]

ergawy wrote:

I can take a look tomorrow unless @JonChesterfield wants to do that himself (since he has substantially more experience with this part of the code than me).

https://github.com/llvm/llvm-project/pull/124089