[OPENMP][NVPTX]Add NVPTX specific definitions for new/delete operators.

Summary:
To use new/delete in NVPTX code we need to define them. Implementation
copied from CUDA wrappers.

Reviewers: hfinkel, jdoerfert

Subscribers: mgorny, guansong, kkwli0, caomhin, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73128