If that example (eval.c) is supposed to be bad, I don't think there's a strong case here. It looks like lots of older Unix/BSD code, and most of the ifdefs are feature-related, rather than platform hacks; some of the functions are a bit long, but that's typical in older C code.

I've never read the vim code before and I was surprised how cleanly written and well-commented it is, given my expectations set by this thread.