doc: only U+FEFF is a byte-order mark; U+FFFE is not

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/9103046
regexp: doc fix

This must have been from when "error" was a good variable
name for an "os.Error". But we use "err" these days.

R=golang-dev, dsymonds, r
CC=golang-dev
https://codereview.appspot.com/9132045
cmd/ld: add .note.GNU-stack section for external linking
Fixes issue 5392.

R=iant, r
CC=golang-dev
https://codereview.appspot.com/9119043
runtime/cgo: fix build for ARM

TBR=iant
CC=golang-dev
https://codereview.appspot.com/9048048