[llvm] [AMDGPU] Support preloading hidden kernel arguments (PR #98861)

[Austin Kerbow via llvm-commits]

kerbowa wrote:

WIP since I still have some concerns about the function cloning and whether we can do it in a function pass properly, and also about having what are essentially reserved parameter name prefixes. I'm thinking about adding metadata so that a conflict wouldn't break anything - otherwise we would need to explicitly disallow conflicts with reserved names, but I'm not doing that currently.

https://github.com/llvm/llvm-project/pull/98861