[libc] Update the AMDGPU implementation to use code object 5 (#72580)

Summary:
This patch includes the necessary changes to make the `libc` tests
running on AMD GPUs run using the newer code object version. The 'code
object version' is AMD's internal ABI for making kernel calls. The move
from 4 to 5 changed how we handle arguments for builtins such as
obtaining the grid size or setting up the size of the private stack.

Fixes: https://github.com/llvm/llvm-project/issues/72517