Fix for CUDA Error "no kernel image"

[pyramid3d]

When running with a clean compile I get this error:

Starting...
ERROR /data/transfer/HashDAG/src/dag_tracer.cu:135: cuda error "no kernel image is available for execution on the device"

This because my hardware only supports CUDA compute capability 5.0.
Adding the following lines to CMakeLists.txt and clean compiling resolves the issue. This will make sure that various compute capacity images are generated:

if(NOT DEFINED CMAKE_CUDA_ARCHITECTURES)
  set(CMAKE_CUDA_ARCHITECTURES 35 50 61 72)
endif()

On a side note: Setting the -gencode arch=compute_50,code=sm_50 flags to the correct version is not removing the error.