test: match gccgo error messages

test: match gccgo error messages

bug340.go:14:7: error: expected type
bug340.go:15:4: error: reference to undefined field or method ‘x’

bug350.go:12:1: error: redefinition of ‘m’
bug350.go:11:1: note: previous definition of ‘m’ was here
bug350.go:15:1: error: redefinition of ‘p’
bug350.go:14:1: note: previous definition of ‘p’ was here

bug351.go:12:6: error: non-name on left side of ‘:=’

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5127041