cmd/gc: skip over reported BOMs
cmd/gc: skip over reported BOMs

This keeps the BOM runes from causing other errors.

R=golang-dev, remyoudompheng
CC=golang-dev
http://codereview.appspot.com/6625062
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go