Allow CUDA compilation for onnxruntime
This small MR allows for onnxruntime to be compiled for use on GPUs via CUDA. As long as CUDA and CUDNN is installed on the compiling machine, a GPU does not need to be physically present, though the CUDA and CUDNN install paths are currently hard coded as:
CUDA_HOME: /usr/local/cuda CUDNN_HOME: /usr/
which may not be correct on all machines.
As is, an extra CMake build flag "ATLonnxruntime_USE_CUDA" is added to enable CUDA compilation. Currently the default behavior is to only compile for CPU as before.