doc: don't invoke go build with -o /dev/null during test
doc: don't invoke go build with -o /dev/null during test

Fixes Issue 5998.

R=golang-dev, khr
CC=golang-dev
https://codereview.appspot.com/12149043

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

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