gopack: remove warning from the use of mktemp
gopack: remove warning from the use of mktemp

gcc-4.6 considers mktemp to be racey

R=golang-dev, rsc, iant
CC=golang-dev
http://codereview.appspot.com/4602050

Committer: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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