[llvm] [AMDGPU][LTO] Introduce AMDGPUCloneModuleLDS (PR #89683)

[Jon Chesterfield via llvm-commits]

JonChesterfield wrote:

Cloning functions can improve LDS allocation in exchange for degrading code density. Seems moderately unlikely to be a win overall to me. Better if there are other reasons to clone the function.

Cloning LDS variables without cloning functions, prior to the existing lowering pass, will not improve codegen and stands a decent chance of making it worse.

https://github.com/llvm/llvm-project/pull/89683