The header file checks 2 things.
* __NVCC__: if the compiler is from NVIDIA
* __CUDACC__: if the source code is CUDA(.cu) file
Since we can't sure all users prefer latest, Version for
`find_pacakge(CUDA)` is downgraded to 9.0.
This is the minimum version for C++14 in CUDA
Current test is only for Windows(cl.exe).
Need to test more with the other host compilers...
* Activate the test when `find_package(CUDA)` worked
* The test runs with C++14
Detailed comments in 'test/cuda-test'
