[release-branch.r58] gofix: fixes for os/signal changes

««« CL 4630056 / 8fe2bc5c3d53
gofix: fixes for os/signal changes

Fixes #1971.

R=adg, rsc
CC=golang-dev
https://golang.org/cl/4630056

»»»

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/4645071