test: Match gccgo error messages.

With the recursive descent parser that gccgo uses, I think
that it doesn't make sense to try to match a statement where a
statement is not expected.  If the construct is not a
statement, you will just get bizarre error messages.

topexpr.go:9:1: error: expected declaration
topexpr.go:14:1: error: expected declaration
topexpr.go:19:1: error: expected declaration

R=rsc, r2
CC=golang-dev
https://golang.org/cl/2175041

test/syntax/topexpr.go

@@ -6,15 +6,15 @@
 
 package main
 
-fmt.Printf("hello")	// ERROR "non-declaration statement outside function body"
+fmt.Printf("hello")	// ERROR "non-declaration statement outside function body|expected declaration"
 
 func main() {
 }
 
-x++	// ERROR "non-declaration statement outside function body"
+x++	// ERROR "non-declaration statement outside function body|expected declaration"
 
 func init() {
 }
 
-x,y := 1, 2	// ERROR "non-declaration statement outside function body"
+x,y := 1, 2	// ERROR "non-declaration statement outside function body|expected declaration"