get correct number of cores info in MacOSX

no /proc file system in MacOSX. use sysctl to return correct number of
cores to speed up building.

Change-Id: Ic813521c5867fd3c5ac1f565894dcb89aa1a3579
The greenhouse effect

Mix some thermal radiation with some greenhouse gases and you have
yourself a nice greenhouse effect.

Change-Id: Ib9ae88536798ca938f39c019c2aa41d812379759