libmach: fix build (set and not used)
libmach: fix build (set and not used)

TBR=golang-dev
CC=golang-dev
https://codereview.appspot.com/7401053

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