Bindgen crashes on enums mixed with macros (#define)

Example of problematic definition:

```C
enum XML_Status {
  XML_STATUS_ERROR = 0,
#define XML_STATUS_ERROR XML_STATUS_ERROR
  XML_STATUS_OK = 1,
#define XML_STATUS_OK XML_STATUS_OK
  XML_STATUS_SUSPENDED = 2
#define XML_STATUS_SUSPENDED XML_STATUS_SUSPENDED
};
```

See: https://github.com/libexpat/libexpat/blob/master/expat/lib/expat.h#L70