test: match gccgo error strings.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/10468043
diff --git a/test/const6.go b/test/const6.go
index c04435d..c005ac3 100644
--- a/test/const6.go
+++ b/test/const6.go
@@ -19,12 +19,12 @@
 	c4 mybool = c2 == (1 < 2)
 	c5 mybool = 1 < 2
 	c6 mybool1 = x < y
-	c7 = c1 == c2 // ERROR "mismatched types"
-	c8 = c2 == c6 // ERROR "mismatched types"
-	c9 = c1 == c6 // ERROR "mismatched types"
+	c7 = c1 == c2 // ERROR "mismatched types|incompatible types"
+	c8 = c2 == c6 // ERROR "mismatched types|incompatible types"
+	c9 = c1 == c6 // ERROR "mismatched types|incompatible types"
 	_ = c2 && (x < y)
 	_ = c2 && (1 < 2)
-	_ = c1 && c2 // ERROR "mismatched types"
-	_ = c2 && c6 // ERROR "mismatched types"
-	_ = c1 && c6 // ERROR "mismatched types"
+	_ = c1 && c2 // ERROR "mismatched types|incompatible types"
+	_ = c2 && c6 // ERROR "mismatched types|incompatible types"
+	_ = c1 && c6 // ERROR "mismatched types|incompatible types"
 )