Recognize gccgo error message.

bug022.go:8:13: error: attempt to index object which is not array, string, or map

R=rsc
DELTA=1  (0 added, 0 deleted, 1 changed)
OCL=31082
CL=31089

test/fixedbugs/bug022.go

@@ -9,7 +9,7 @@ package main
 func putint(digits *string) {
 	var i byte;
 	i = (*digits)[7];  // compiles
-	i = digits[7];  // ERROR "illegal"
+	i = digits[7];  // ERROR "illegal|is not"
 }
 
 func main() {