preamble/ptrdiff: order int types by likeliness

We are most likely on a platform that uses 64-bit pointers.

Expectably, 16-bit pointers are not a realistic target for ctypesgen,
but retain it anyways to be C standard correct.

Note, the point of this template is to achieve universal bindings. If
bindings were target platform specific, the ptrdiff_t constant pulled in
from stddef.h would be fine.

src/ctypesgen/printer_python/preamble.py

@@ -2,10 +2,10 @@
 from ctypes import *  # noqa: F401, F403
 
 def _get_ptrdiff_t():
-    int_types = [ctypes.c_int16, ctypes.c_int32]
+    int_types = [ctypes.c_int32, ctypes.c_int16]
     # Some builds of ctypes do not provide c_int64. Assumably, this means the platform doesn't have 64-bit pointers.
     if hasattr(ctypes, "c_int64"):
-        int_types.append(ctypes.c_int64)
+        int_types.insert(0, ctypes.c_int64)
     return next((t for t in int_types if sizeof(t) == sizeof(c_size_t)), None)
 
 c_ptrdiff_t = _get_ptrdiff_t()