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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

I can confirm that it passes the tests against the `libc` targets, namely basic `stdarg.h` implementations and `sprintf`.

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