Serialization of dynamically defined guvectorize numba functions results in a segfault.

> ### Note:
> This issue is related to an issue posted to the page of joblib; see https://github.com/joblib/joblib/issues/1042.

## Problem description
I would like to pickle dynamically defined functions which use the guvectorize decorator from numba. However, this results in a segmentation fault. If it is not possible to pickle these objects then a better error message would be greatly appreciated.

## Minimal Example

### Software
- Ubuntu 19.04
- python=3.7
- numba=0.49.1
- numpy=1.18.5
- cloudpickle=1.4.1

```python
import cloudpickle
import numpy as np
from numba import guvectorize

@guvectorize(
["f8[:], f8[:]"], "(n) -> ()", nopython=True
)
def func(a, out):
out_ = a.sum()
out[0] = out_

pickled_func = cloudpickle.dumps(func)
```

### Error
```bash
13994 segmentation fault (core dumped)
```