And enable PIE in cmd/go because that's all it seems to take.

Change-Id: Ie017f427ace5e91de333a9f7cba9684c4641dfd5
Reviewed-on: https://go-review.googlesource.com/14222Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>