Empty program will sometimes do a major GC, sometimes not - figure out why

[sjamaan]

This is an interesting thing to figure out

If you compile a completely empty file, and run it with -:g, sometimes it will do a major GC and sometimes it won't (just run it a few times, you'll notice the output is different sometimes).

Also, the major GC count is always at least 1.

This might also contribute to the instability of our benchmark results.