Keep unused CPU cores busy during unit benchmarking

[dictoon]

From Prime95's source code:

/* Keep CPU cores busy.  This should prevent "turbo boost" from kicking in. */
/* We do this to hopefully produce more consistent benchmarks.  We don't want to report */
/* a CPU speed of 1.87 GHz and then produce a benchmark running at a boosted 3.2 GHz */
/* (this happens on a Core i7 Q840M processor). */