[CUDA][HIP] Fix host/device check with -fopenmp

[CUDA][HIP] Fix host/device check with -fopenmp

CUDA/HIP program may be compiled with -fopenmp. In this case, -fopenmp is only passed to host compilation
to take advantages of multi-threads computation.

CUDA/HIP and OpenMP both use Sema::DeviceCallGraph to store functions to be analyzed and remove them
once they decide the function is sure to be emitted. CUDA/HIP and OpenMP have different functions to determine
if a function is sure to be emitted.

To check host/device correctly for CUDA/HIP when -fopenmp is enabled, there needs a unified logic to determine
whether a function is to be emitted. The logic needs to be aware of both CUDA and OpenMP logic.

Differential Revision: https://reviews.llvm.org/D67837

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374263 91177308-0d34-0410-b5e6-96231b3b80d8