[OpenMP][NVPTX] Replaced CUDA builtin vars with LLVM intrinsics

Replaced CUDA builtin vars with LLVM intrinsics such that we don't need
definitions of those intrinsics.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D95013

GitOrigin-RevId: fd70f70d1e02752f411fcf923fddda31cce376ae
1 file changed