cmd/vet: add assembly checker

Fixes issue 5036.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/7531045
database/sql: add missing []byte and RawBytes conversions

E.g conversions from numeric types to RawBytes are missing, what makes RawBytes unusable in some cases.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7783046

Committer: Brad Fitzpatrick <bradfitz@golang.org>
runtime/cgo, go/build: re-enable cgo for FreeBSD/ARM.

R=dave, rsc
CC=golang-dev
https://codereview.appspot.com/7970043