GPU Updates, master branch (2020.08.14.)

This MR goes hand-in-hand with athena!35624 (merged).

The update in FindSYCL.cmake makes it possible to build code for NVidia cards with the latest DPC++ versions, while making the code a bit more flexible against possible further changes in naming in the future. (See: https://github.com/intel/llvm/issues/2164)

The CUDA compilation flag updates are here to:

• Specify explicitly what C++ standard to build CUDA with;
• Silence warnings from CMake 3.18+ when building CUDA code (See: https://cmake.org/cmake/help/git-stage/prop_tgt/CUDA_ARCHITECTURES.html).