Build fixes for OpenBSD

The commits here lets everything build and run on OpenBSD.  There is no /proc on OpenBSD so Sys_CPUCount() thinks there is one processor.  This could be later changed to use sysctl (hw.ncpu) similiar to platform_osx, or perhaps a sysconf(3) fallback with _SC_NPROCESSORS_ONLN could be used.  The cpu frequency could also be pulled from sysctl, but these changes don't seem to be strictly required to get things running.

And though there is an bug report open on Mesa, Mesa seems to work here:

OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) Ivybridge Mobile
OpenGL core profile version string: 3.2 (Core Profile) Mesa 10.2.3
OpenGL core profile shading language version string: 3.30
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile

OpenGL version string: 3.0 Mesa 10.2.3
OpenGL shading language version string: 1.30
OpenGL context flags: (none)

OpenGL ES profile version string: OpenGL ES 3.0 Mesa 10.2.3
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.0

apart from some shader related errors printed to the console along the
lines of:

0:150(19): error: could not implicitly convert operands to arithmetic operator
While compiling fragment program renderprogs/interactionSM.pixel

There is nothing that visually sticks out as wrong when playing.