Setting CUDA_PATH for cupy

[jakirkham]

CuPy looks for the local CUDA install using (in part) the CUDA_PATH environment variable. If possible, it would be nice to set this so it points to cudatoolkit. If not possible, it would be nice to have a post-link script that recommends setting this environment variable.

[jjhelmus]

Is CuPy looking for the CUDA libraries or the nvcc compiler? The former are provided by the cudatoolkit package and a activation script could set CUDA_PATH to point at these. If CuPy needs nvcc this unfortunately is not provided in the cudatoolkit package.

[jakirkham]

Here's the relevant line. It only needs CUDA_PATH; so, an activation script should be fine. It will also look for nvcc if it cannot find CUDA_PATH, but only as a way to find what CUDA_PATH should be.