[release-branch.go1.1] cmd/gc: fix missing slice/array types in export data.

««« CL 9953044 / 0e1b2f7384d2
cmd/gc: fix missing slice/array types in export data.

Fixes #5614.

R=golang-dev
CC=golang-dev
https://golang.org/cl/9953044
»»»

R=iant, remyoudompheng, dsymonds
CC=golang-dev
https://golang.org/cl/10033043