[clang] [libc] [llvm] [libc] Implement (v|f)printf on the GPU (PR #96369)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> > You could theoretically break this if you didn't go through the C ABI and ignored type promotion, but I'm not concerned with that kind of misuse since it's against the ABI in the first place.
> 
> The IR has its own ABI that may or may not match whatever the platform "C ABI' is. Especially given the lack of a formal platform ABI specification, I would not characterize not using the C ABI as misuse or against the ABI

The ABI in this case is what NVIDIA does, figuring out whether or not an argument came from a struct or was passed directly would be a nightmare of metadata nodes so I *really* don't want to go down that path.

https://github.com/llvm/llvm-project/pull/96369