cmd/go: honour buildflags in go run
cmd/go: honour buildflags in go run

Either documentation or implementation
of go run's flags is wrong currently.
This change assumes the documentation
to be right.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/5752054

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go