tools: Don't use distutils in configure or Makefile

Python distutils is deprecated and is going to be removed in Python
3.12.  distutils.sysconfig is available as the sysconfig module in
stdlib since Python 2.7 and Python 3.2, so use that directly.

Update the README to reflect that we now depend on Python 2.7.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Javi Merino <javi.merino@cloud.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
[Regen ./configure]
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

docs/configure

@@ -1986,6 +1986,11 @@ _ACEOF
 XEN_RUN_STORED=$rundir_path/xenstored
 
 
+cat >>confdefs.h <<_ACEOF
+#define XEN_RUN_STORED "$XEN_RUN_STORED"
+_ACEOF
+
+
 XEN_LIB_DIR=$localstatedir/lib/xen