gccgo: bogus incompatible types in binary expression error

gccgo rejects to compile the following program:

``` go
package a
var a, b = 0, a^0/8i
```

```
go.go:2:15: error: incompatible types in binary expression
```

Both gc and go/types compile it.

gcc version 6.0.0 20150702 (experimental) (GCC)
