build: fix noclobber
build: fix noclobber

I got it backwards last time, and somehow
that was leaking into the parent shell?

R=golang-dev, iant
CC=golang-dev
http://codereview.appspot.com/4826054

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