[release-branch.go1.1] cmd/gc: compute initialization order for top-level blank vars too.

««« CL 8601044 / 3a74e15c5d56
cmd/gc: compute initialization order for top-level blank vars too.

Fixes #5244.

R=golang-dev, rsc, iant, r, daniel.morsing
CC=golang-dev
https://golang.org/cl/8601044
»»»

R=iant, rsc
CC=golang-dev
https://golang.org/cl/10250043