Hello!

I have a, potentially edge case, issue with a njited function that utilizes `np.stack`

. A minimum working example is below…

```
import numpy as np
from numba import njit
def f(x, y):
x2 = x**2
y2 = y**2
result = np.stack((x, y))
return result
fn = njit(f)
x_array = np.linspace(0., 10., 5)
y_array = np.linspace(-1., 1., 5)
x_scalar = 10.
y_scalar = -0.5
```

The purely Python implementation returns a 2d array when `f(x_array, y_array)`

is called and a 1d array when calling `f(x_scalar, y_scalar)`

(specifically: `[10. -0.5]`

). The njit’d function works fine for `fn(x_array, y_array)`

but fails for `fn(x_scalar, y_scalar)`

with the error:

```
TypingError: Failed in nopython mode pipeline (step: nopython frontend)
No implementation of function Function(<function stack at 0x000002071A9750D0>) found for signature:
>>> stack(UniTuple(float64 x 2))
```

I am running `numba 0.53.1`

and `numpy 1.19.2`

under `python 3.9.4`

.

Does njit not currently support all of `np.stack`

's features? Thanks for the help!