opencv3: enable pthreads parallel for loops
The WITH_PTHREADS_PF option was errantly categorized as a Windows only option.
WITH_PTHREADS_PF actually enables a parallelization framework that utilizes
pthreads to optimize some inner for loops of different OpenCV operations. This
optimization is available on any platform that has pthreads.
Signed-off-by: bradford barr <bradford@density.io>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>