build: use awk instead of giant egrep regexp
build: use awk instead of giant egrep regexp

Avoids buggy version of egrep on some Macs.

R=r, dsymonds
CC=golang-dev
http://codereview.appspot.com/4603056

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