Unexpected subtraction result for int64 - uint32

```python
>>> import loopy as lp
>>> import numpy as np
>>> knl = lp.make_kernel("{:}", "z = x-y", [lp.GlobalArg("x", dtype=np.int64, shape=()), lp.GlobalArg("y", dtype=np.uint32, shape=()), "..."])
>>> print(knl)
---------------------------------------------------------------------------
KERNEL: loopy_kernel
---------------------------------------------------------------------------
ARGUMENTS:
x: type: np:dtype('int64'), shape: () aspace: global
y: type: np:dtype('uint32'), shape: () aspace: global
z: type: , shape: () aspace: global
---------------------------------------------------------------------------
DOMAINS:
{ : }
---------------------------------------------------------------------------
INAME IMPLEMENTATION TAGS:
---------------------------------------------------------------------------
INSTRUCTIONS:
z = x + (-1)*y {id=insn}
---------------------------------------------------------------------------
>>> knl(q, x=np.array(2), y=np.array(1, dtype=np.uint32))
(, (array(4294967297),))
```