cmd/yacc: don't emit line comment when -l is given Fixes issue 5447.
cmd/yacc: don't emit line comment when -l is given
Fixes issue 5447.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/9343045

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