[release-branch.r58] build: use awk instead of giant egrep regexp

««« CL 4603056 / 655a4be3968f
build: use awk instead of giant egrep regexp

Avoids buggy version of egrep on some Macs.

R=r, dsymonds
CC=golang-dev
https://golang.org/cl/4603056
»»»

R=adg
CC=golang-dev
https://golang.org/cl/4695042