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

[Pierre van Houtryve via cfe-commits]

https://github.com/Pierre-vh approved this pull request.

LGTM if a kill switch is added, I would wait a day more before landing in case anyone else has concerns

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