Optimized signed comparison with zero

[ZERICO2005]

Turn cp a, 0 \ call pe, __setflags \ jp p, .L.foo into or a, a \ jp p, .L.foo

While somewhat related to #37, we should probably update how signed comparisons with zeros are handled. Even if call pe, __setflags is removed, we would still need to convert cp a, 0 into or a, a

__setflags discussion here: https://discordapp.com/channels/432891584451706892/1488273105121185875