[CUDA] provide wrapper functions for new NVCC builtins.

For sm_80 NVCC introduced a handful of builtins with the names that deviate from
the historic __nvvm_/__nv naming convention. Clang/LLVM does provide equivalent
builtins, but using different names. This patch maps NVCC-style builtins to
their clang counterparts.

Differential Revision: https://reviews.llvm.org/D150894