tools/python: change 's#' size type for Python >= 3.10

Python < 3.10 by default uses 'int' type for data+size string types
(s#), unless PY_SSIZE_T_CLEAN is defined - in which case it uses
Py_ssize_t. The former behavior was removed in Python 3.10 and now it's
required to define PY_SSIZE_T_CLEAN before including Python.h, and using
Py_ssize_t for the length argument. The PY_SSIZE_T_CLEAN behavior is
supported since Python 2.5.

Adjust bindings accordingly.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>

tools/python/xen/lowlevel/xc/xc.c

@@ -4,6 +4,7 @@
  * Copyright (c) 2003-2004, K A Fraser (University of Cambridge)
  */
 
+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #define XC_WANT_COMPAT_MAP_FOREIGN_API
 #include <xenctrl.h>
@@ -1774,7 +1775,7 @@ static PyObject *pyflask_load(PyObject *self, PyObject *args, PyObject *kwds)
 {
     xc_interface *xc_handle;
     char *policy;
-    uint32_t len;
+    Py_ssize_t len;
     int ret;
 
     static char *kwd_list[] = { "policy", NULL };

tools/python/xen/lowlevel/xs/xs.c

@@ -18,6 +18,7 @@
  * Copyright (C) 2005 XenSource Ltd.
  */
 
+#define PY_SSIZE_T_CLEAN
 #include <Python.h>
 
 #include <stdbool.h>
@@ -141,7 +142,7 @@ static PyObject *xspy_write(XsHandle *self, PyObject *args)
     char *thstr;
     char *path;
     char *data;
-    int data_n;
+    Py_ssize_t data_n;
     bool result;
 
     if (!xh)