Fix two compiler warnings on Win64.

Modules/_ctypes/_ctypes.c

@@ -1477,7 +1477,7 @@ SimpleType_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 	StgDictObject *stgdict;
 	PyObject *proto;
 	const char *proto_str;
-	int proto_len;
+	Py_ssize_t proto_len;
 	PyMethodDef *ml;
 	struct fielddesc *fmt;
 

Modules/_ctypes/libffi_msvc/prep_cif.c

@@ -163,7 +163,7 @@ ffi_status ffi_prep_cif(/*@out@*/ /*@partial@*/ ffi_cif *cif,
 	    bytes = ALIGN(bytes, (*ptr)->alignment);
 	  
 #endif
-	  bytes += STACK_ARG_SIZE((*ptr)->size);
+	  bytes += (unsigned)STACK_ARG_SIZE((*ptr)->size);
 	}
 #endif
     }