cmd/ld: replace -hostobj with -linkmode

Still disabled. Need to fix TLS.

R=golang-dev, minux.ma, bradfitz
CC=golang-dev
https://codereview.appspot.com/7783044
misc/dashboard: show correct dir name in README

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7909043