This commit improves x86 assembly code with speed and size optimizations, mainly consisting on:
- mov <reg>, 0 => xor <reg>, <reg>. When flags are not used it is usually smaller, and faster in 386 or lower CPU.
- cmp <reg>, 0 => test <reg>, <reg>. When flags are not used it is usually smaller, and faster in 386 or lower CPU.
- mov <reg>, -1 => or <reg>, -1. When flags are not used it is usually smaller, and faster in 386 or lower CPU.
- mov <regh>, x, mov <regl>, y => mov regx, x*256+y. Usually smaller and always faster.

Special focus has been put on mathlib and clib. Commit builds OK, and passes all regression tests.

More optimizations would follow.