nbody: implement CUDA-less build variant

Adds a dummy wrapper API for most of the CUDA calls when built with -DNO_CUDA.
This can be enabled via 'make NO_CUDA=1'.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
nbody_CPU_SSE_threaded: make sseWorkerThread a static function

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
nbody: implement OpenMP variant

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
nbody: eliminate 'N % g_numCPUCores' check

This causes the app to not function if the system's CPU count is not a power of
two. I have a 24-thread Westmere box which it decided to not function on.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
nbody: clean up printout format if/when user hits a hotkey

Signed-off-by: Steven Noonan <steven@uplinklabs.net>