config: Add a --without-python option to build process

Add the ability to build libgem5 without embedded Python or the
ability to configure with Python.

This is a prelude to a patch to allow config.ini files to be loaded
into libgem5 using only C++ which would make embedding gem5 within
other simulation systems easier.

This adds a few registration interfaces to things which cross
between Python and C++.  Namely: stats dumping and SimObject resolving

src/python/swig/pyobject.cc

@@ -157,9 +157,12 @@ extern "C" SimObject *convertSwigSimObjectPtr(PyObject *);
 // these in sim/main.cc as well that are handled without this define.
 #define PCC(s)  const_cast<char *>(s)
 
+/** Single instance of PythonSimObjectResolver as its action is effectively
+ *  static but SimObjectResolver can use a non-persistent object */
+PythonSimObjectResolver pythonSimObjectResolver;
 
 SimObject *
-resolveSimObject(const string &name)
+PythonSimObjectResolver::resolveSimObject(const string &name)
 {
     PyObject *module = PyImport_ImportModule(PCC("m5.SimObject"));
     if (module == NULL)
@@ -188,3 +191,9 @@ resolveSimObject(const string &name)
 
     return obj;
 }
+
+Checkpoint *
+getCheckpoint(const std::string &cpt_dir)
+{
+    return new Checkpoint(cpt_dir, pythonSimObjectResolver);
+}