[dev.power64] cmd/9a: use liblink, add required additional instructions.

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://codereview.appspot.com/127730043
[dev.power64] cmd/9l: update header files for liblink

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://codereview.appspot.com/128720044