Teach vtkMathConfigure about nvcc support for std::isnan and friends.

The CUDA compiler(nvcc) is a secondary compiler that is used beside your host
compiler. While your host compiler can support std::isnan and other functions,
the CUDA compiler doesn't. Because the CUDA compiler is given both host and
device code to parse it will then fail when it sees std::isnan because it is
in the vtkMath header and not the implementation file. To get around this
issue we check __CUDACC__ which is only set when we are compiling with the
CUDA compiler

Change-Id: Ifadf476937617cce382e52a0546f77e8044b6630
Merge topic 'vtkMath_support_cuda' into master

4646c7be Teach vtkMathConfigure about nvcc support for std::isnan and friends.