cmd/gc: fix crash in -live mode
cmd/gc: fix crash in -live mode

debuglive >= 1 is not the condition under which we
start recording messages (we avoid printing for
init functions even if debuglive is set).

LGTM=bradfitz, iant
R=golang-codereviews, bradfitz
CC=golang-codereviews, iant, khr
https://codereview.appspot.com/74390043

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang