Loopy's host-side shape inference cannot solve system of equations

```python
knl = lp.make_kernel(
"{[i, j]: 0<=i<(2*n + 3*m + 2) and 0<=j<(6*n + 4*m + 3)}",
"""
out = sum([i, j], A[i, j])
""")

knl(cq, A=np.random.randn(20, 37))
```

fails with
```
File "", line 52, in invoke_loopy_kernel_loopy_kernel
TypeError: value argument 'm' was not given and could not be automatically determined
```

Loopy couldn't infer that `n=3, m=4` corresponds from A's shape.