cmd/gc: inlining of variadic functions.
cmd/gc: inlining of variadic functions.

R=rsc, lvd, golang-dev, kardianos
CC=golang-dev
https://codereview.appspot.com/7093050
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go