When creating new project, you should tell project wizard that you want floating point. Wizard then adds required library. What library to add is specified in <CW intall folder>\lib\hc12c\readme.txt
BTW, S12 is 16-bit MCU. Please use right forum next time. Keep in mind that there are dedicated Codewarrior forums. This thread should be in "Codewarrior 8- adn 16- bit"