This function is not available on platforms that do not implement the underlying C function. Included in this would be MaxOS[1], and FreeBSD[2]
[1] : http://opensource.apple.com//source/xnu/xnu-1456.1.26/bsd/sys/signal.h
[2] : http://fxr.watson.org/fxr/source/sys/signal.h?v=FREEBSD11