Fix compilation warnings on Windows (GH-8627)

Fix compilation warnings on Windows (GH-8627)

* Fix compilation warning in _ctypes module on Window

(cherry picked from commit 20f11fe43c47b68c8b9dd6539d2d40b66c9957f9)

* Fix compilation warnings on Windows 64-bit

(cherry picked from commit 725e4212229bf68f87d4f66c1815d444ddfc7aa5)

* Fix compiler warning in unicodeobject.c

Explicitly case to Py_UNICODE to fix the warning:

Objects\unicodeobject.c(4225): warning C4244: '=' :
conversion from 'long' to 'Py_UNICODE', possible loss of data

The downcast cannot overflow since we check that value <= 0x10ffff.