Thread: warning: implicit declaration of function `sigset', `sighold' & `sigrelse'

OK, I almost have this thing building cleanly, but I'm seeing these warnings:

Code:

warning: implicit declaration of function `sigset'
warning: implicit declaration of function `sighold'
warning: implicit declaration of function `sigrelse'

Even though that .c file includes <signal.h>
Am I missing something, or does RedHat Enterprise 3.0 not support those functions?