test: Match gccgo error messages.

named1.go:40:11: error: argument 1 has incompatible type (cannot use type bool as type Bool)
named1.go:41:11: error: argument 1 has incompatible type (cannot use type bool as type Bool)
named1.go:43:7: error: incompatible types in assignment (cannot use type bool as type Bool)
named1.go:44:12: error: argument 4 has incompatible type (cannot use type Bool as type bool)
named1.go:46:4: error: incompatible types in assignment (cannot use type bool as type Bool)
named1.go:48:11: error: argument 1 has incompatible type (cannot use type bool as type Bool)
named1.go:50:7: error: incompatible types in assignment (cannot use type bool as type Bool)
named1.go:54:7: error: incompatible types in assignment (cannot use type bool as type Bool)
named1.go:60:7: error: incompatible types in assignment (cannot use type bool as type Bool)
named1.go:63:9: error: argument 1 has incompatible type (cannot use type bool as type Bool)
named1.go:64:4: error: incompatible types in assignment (cannot use type bool as type Bool)
named1.go:67:17: error: invalid type conversion (cannot use type Slice as type String)

R=rsc
CC=golang-dev
https://golang.org/cl/2146044

test/named1.go

@@ -64,5 +64,5 @@ func main() {
 	b = closed(c)     // ERROR "cannot use.*type bool.*type Bool"
 	_ = b
 
-	asString(String(slice)) // ERROR "cannot convert slice"
+	asString(String(slice)) // ERROR "cannot .*type Slice.*type String"
 }