CUDA Linux build + package issues

[tbirdso]

Discussed in #35:

• Failure to find Threads library on Linux
• Failure to link with -lcuda when building Python wheels on Linux (tested with Python 3.8.5)

[tbirdso]

Related to #21

[tbirdso]

Suggested: Build against CuPy packages as dependency

https://pypi.org/project/cupy/

https://developer.nvidia.com/cuda-python#:~:text=CUDA%C2%AE%20Python%20provides%20Cython,achieve%20faster%20results%20and%20accuracy.

https://rapids.ai/

https://docs.cupy.dev/en/stable/install.html

[thewtex]

@jakirkham is the expert wizard here! 🧙‍♂️ @jakirkham what do you recommend in terms of building against CUDA so this package is compatible with CUDA Python? Weak linking to cuda? Is there something specific we should build against?

[SimonRit]

In RTK, we intend to release Cuda packages soon, see SimonRit/RTK#488. We assume that the user has Cuda installed and have no dependency on a Cuda Python package... I was under the impression that this is standard practice but I might be wrong. cc @LucasGandel