[clang] [libc] [llvm] [AMDGPU] Implement variadic functions by IR lowering (PR #93362)

[Jon Chesterfield via llvm-commits]

JonChesterfield wrote:

I've spawned #93974 in case we can land the target independent part in parallel with me trying to debug the amdgpu/libc error. Maintaining different branches with different variations on what subset is implemented is confusing me quite a lot and leads to reviewers seeing essentially the same code repeatedly - I haven't found a way to represent base + N extensions in github without landing the base commit first.

https://github.com/llvm/llvm-project/pull/93362