improve corpus used to calculate fitness

[WestleyArgentum]

Right now the micro-benchmarks that come with Julia are used to evaluate the fitness (speed) of pass layouts. This has a bunch of potential problems, and raises some interesting questions.

Should we try to find a layout that optimizes naively-written julia well?
Or should we focus on finding one that makes julia written to be performant as fast as possible?
Will the best layout be the same in both cases?

Is it possible to come up with a small, relatively quick-running set of benchmarks that would still be representative as fitness tests? Because the algorithm has to run fitness test one-by-one, this could help tremendously with speeding up the search.