test: add a couple of cases to const1.go that crashed gccgo
R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5713045
diff --git a/test/const1.go b/test/const1.go
index f944cde..bc399c0 100644
--- a/test/const1.go
+++ b/test/const1.go
@@ -43,7 +43,9 @@
b3 = Uint8 - Uint8 // OK
b4 = Uint8 - Uint8 - Uint8 // ERROR "overflow"
b5 = uint8(^0) // ERROR "overflow"
+ b5a = int64(^0) // OK
b6 = ^uint8(0) // OK
+ b6a = ^int64(0) // OK
b7 = uint8(Minus1) // ERROR "overflow"
b8 = uint8(int8(-1)) // ERROR "overflow"
b8a = uint8(-1) // ERROR "overflow"
