gccgo: does not convert untyped complex 0i to int in binary operation involving an int

gc successfully compiles the following program:

``` go
package a
var e,f = f^0i,0
```

while gccgo says:

```
go.go:2:12: error: incompatible types in binary expression
```

gccgo seems to be right, because 0i is imaginary literal.

go version devel +bb7e665 Tue Jun 30 07:42:37 2015 +0000 linux/amd64
