misc/cgo/test: fix darwin build
misc/cgo/test: fix darwin build

uuid_t is defined in unistd.h on OS X, unfortunately.

R=iant, rsc
CC=golang-dev
http://codereview.appspot.com/6455057

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