[llvm] [AMDGPU] support lib call (PR #74741)

[Pierre van Houtryve via llvm-commits]

https://github.com/Pierre-vh commented:

I think that deleting unused lib functions is overkill, you can probably make this patch much simpler by just setting the libcall name & fixing it so it can find it, no?

It'd make the patch much less intrusive and more likely to be accepted as a short-term fix while we determine if we want to use some other system (like expanding in IR) or refine libcalls for long-term usage.

https://github.com/llvm/llvm-project/pull/74741