Hi,
please check the following link: http://stackoverflow.com/questions/2418157/ubuntu-linux-c-error-undefined-reference-to-clock-gettime-and-clock-settim
you have to make sure you add the -lrt to the linker. This function, however, is not necessary. If anything, you could just remove the contents of the function. I will make sure I build fuzzylite in additional Linux platforms for the next version.
Cheers.