python: Add fallbacks for packages that have been renamed

Python 3 has restructured some packages. Specifically, __builtin__ has
been renamed to builtins and urlparse has been included in urllib.

Change-Id: I81f8f3942471db1043006a36abbad6e5a49e0a43
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15994
Reviewed-by: Juha Jäykkä <juha.jaykka@arm.com>

src/python/m5/util/code_formatter.py

@@ -26,7 +26,11 @@
 
 from __future__ import print_function
 
-import __builtin__
+try:
+    import builtins
+except ImportError:
+    # Python 2 fallback
+    import __builtin__ as builtins
 import inspect
 import os
 import re
@@ -66,8 +70,8 @@ class lookup(object):
         if self.formatter.globals and item in self.frame.f_globals:
             return self.frame.f_globals[item]
 
-        if item in __builtin__.__dict__:
-            return __builtin__.__dict__[item]
+        if item in builtins.__dict__:
+            return builtins.__dict__[item]
 
         try:
             item = int(item)