Summary:
This patch switches the GPU utility helpers to wrapping around the
gpuintrin.h ones with a C++ flavor.

Summary:
Currently fails to build libc++ because this is missing.

This is a part of #97655.

Reverts llvm/llvm-project#98075

bots are broken

This is a part of #97655.

Summary:
Recent patches have added solutions to the remaining sources of
divergence. This patch simply removes the last occures of things like
`has_builtin`, `ifdef` or builtins with feature requirements. The one
exception here is `nanosleep`, but I made changes in the
`__nvvm_reflect` pass to make usage like this actually work at O0.

Depends on https://github.com/llvm/llvm-project/pull/81331

Summary:
The GPU `nanosleep` tests would occasionally fail. This was due to the
fact that we used integer division to determine how many ticks we had to
sleep for. This would then truncate, leaving us with a value just
slightly below the requested value. This would then occasionally leave
us with a return value of `-1`. This patch just changes the code to
round up by 1 so we always sleep for at least the requested value.

Summary:
Recent patches have implemented builitin versions of these functions.
This patch simply removes uses of inline assembly to hopefully improve
optimizations in this area.

This is step 4 of
https://discourse.llvm.org/t/rfc-customizable-namespace-to-allow-testing-the-libc-when-the-system-libc-is-also-llvms-libc/73079