Makefile `-gencode` only embed ptx

[ptheywood]

The CUDA Makefile throughout the many, many branches of this repository only embed SM_35 PTX, they do not compile for any "real" architectures.

NVCC_FLAGS= -gencode arch=compute_35,code=compute_35

This means they will always preform PTX JIT, even when running on an SM_35 device, resulting in wait time and potentially less useful error messages (I.e. if too much constant cache is requested, the error is just a ptx jit compilation failed).

Instead, IMO it should always requrest a real and virtual arch as a minimum:

e.g.

NVCC_FLAGS= -gencode arch=compute_35,code=sm_35 arch=compute_35,code=compute_35

or

NVCC_FLAGS= -gencode arch=compute_35,code=[sm_35,compute_35]

are some of the many ways this could be achieved.

NVCC docs

[Robadob]

Same change probably useful for visual studio too, whereby sm_52, sm_52 is not working on sm_61.