Error for syscall.Errno

I encountered an error with `syscall.Errno` (defined as `uintptr`):
```go
var err syscall.Errno
_, herr := hashstructure.Hash(err, hashstructure.FormatV2, nil)
```

```text
binary.Write: invalid type syscall.Errno
```

I could test for that but I'm wondering what kind of restrictions I should assume for calling `hashstructure.Hash`.