FASM

FASM is a fast assembly language compiler for the x86 architecture processors, which does multiple passes to optimize the size of generated machine code. It is self-compilable and versions for different operating systems are provided. All the versions are designed to be used from the system command line and they should not differ in behavior. This program is writed by Tomasz Grysztar.

Emerge
To install :

Usage
To get information about optional settings after compilation, just type this command in terminal: