test: Recognize gccgo error messages.

bug255.go:11: error: array bound truncated to integer
bug255.go:12: error: array bound is not numeric
bug255.go:13: error: array bound is not numeric
bug255.go:14: error: array bound is not constant
bug255.go:15: error: array bound overflows

R=rsc
CC=golang-dev
https://golang.org/cl/2091042

test/fixedbugs/bug255.go

@@ -9,7 +9,7 @@ package main
 var a [10]int	// ok
 var b [1e1]int	// ok
 var c [1.5]int	// ERROR "truncated"
-var d ["abc"]int	// ERROR "invalid array bound"
-var e [nil]int	// ERROR "invalid array bound"
-var f [e]int	// ERROR "invalid array bound"
+var d ["abc"]int	// ERROR "invalid array bound|not numeric"
+var e [nil]int	// ERROR "invalid array bound|not numeric"
+var f [e]int	// ERROR "invalid array bound|not constant"
 var g [1<<65]int	// ERROR "overflows"