[clang] [AMDGPU][clang] provide device implementation for __builtin_logb and … (PR #129347)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> The motivation came from CUDA cccl code containing __builtin_logb and __builtin_scalbn and being able to handle them.

In my ideal world, unhandled builtins would be lowered before the linker and we'd have a working library called `libm.a` that matches the platform.

https://github.com/llvm/llvm-project/pull/129347