[dev.power64] cmd/9c: use liblink, use Go argument passing rules, support both endians

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://codereview.appspot.com/126800043
[dev.power64] .hgignore: update for the 9 toolchain

LGTM=dave, rsc
R=rsc, iant, dave
CC=golang-codereviews
https://codereview.appspot.com/124840043