libmach: trivial: resolve unused parameter warnings
libmach: trivial: resolve unused parameter warnings

Fix a bunch of warnings detected by https://codereview.appspot.com/8090044.

Same as CL 10483044, but for FreeBSD.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/10498044

pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,gnanderson/go,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,gnanderson/go,apparentlymart/golang,gnanderson/go,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,tv42/old-go,apparentlymart/golang,tv42/old-go,gnanderson/go,tv42/old-go,gnanderson/go,tv42/old-go,gnanderson/go