cmd/cgo: change GoStringN and GoBytes from intgo to int32
cmd/cgo: change GoStringN and GoBytes from intgo to int32

Fixes build.

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/9667047

wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,firebitsbr/golang-old