test: match gccgo error messages for bug323.go.

bug323.go:18:3: error: reference to undefined field or method ‘Meth’
bug323.go:19:3: error: reference to undefined field or method ‘Meth2’

R=golang-dev, rsc1
CC=golang-dev
https://golang.org/cl/4280072

test/fixedbugs/bug323.go

@@ -15,6 +15,6 @@ func (t T) Meth2() {}
 func main() {
 	t := &T{}
 	p := P(t)
-	p.Meth()  // ERROR "undefined \(type P"
-	p.Meth2() // ERROR "undefined \(type P"
+	p.Meth()  // ERROR "undefined"
+	p.Meth2() // ERROR "undefined"
 }