Add a CUDA test

test cuda: import fmt in CUDA source code

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'

test cuda: add more comment / macro check

* checks both `__NVCC__` and `__CUDACC__`

More comments for CMake and CUDA source file.

test cuda: <fmt/core.h> checks NVCC and CUDA

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

test/cuda-test/cuda-cpp14.cu

@@ -0,0 +1,28 @@
+//  Direct NVCC command line example:
+//
+//  nvcc ./cuda-cpp14.cu -x cu -I"../include" -l"fmtd" -L"../build/Debug" \
+//       -std=c++14 -Xcompiler /std:c++14 -Xcompiler /Zc:__cplusplus
+
+// Ensure that we are using the latest C++ standard for NVCC
+// The version is C++14
+//
+// https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#c-cplusplus-language-support
+// https://en.cppreference.com/w/cpp/preprocessor/replace#Predefined_macros
+static_assert(__cplusplus >= 201402L, "expect C++ 2014 for nvcc");
+
+#include <fmt/core.h>
+
+#include <cuda.h>
+#include <iostream>
+
+extern auto make_message_cpp() -> std::string;
+extern auto make_message_cuda() -> std::string;
+
+int main() {
+  std::cout << make_message_cuda() << std::endl;
+  std::cout << make_message_cpp() << std::endl;
+}
+
+auto make_message_cuda() -> std::string {
+  return fmt::format("nvcc compiler \t: __cplusplus == {}", __cplusplus);
+}