[llvm] [AMDGPU] Run LowerLDS at the end of the fullLTO pipeline (PR #75333)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

Just a thought: if we're not okay with changing the order of LowerModuleLDS for gpu-rdc (because this affects all full LTO builds), I can try adding a parameter to the callback to tell us if we're doing module splitting or not, and if we're not, we just run things as usual.

https://github.com/llvm/llvm-project/pull/75333