runtime: fix FreeBSD build
runtime: fix FreeBSD build

stab in the dark but plausible: the kernel does try to
return time zone information.
http://fxr.watson.org/fxr/source/kern/kern_time.c?v=FREEBSD8#L421

R=iant
CC=golang-dev
http://codereview.appspot.com/206053

firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,wesolows/golang