scons: Fixes to improve python 3 support.

Some simple fixes to improve python 3 compatability in scons.

Change-Id: I89aba6ed9d73ee733307c57e033c636029d9cb7a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23264
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>

site_scons/site_init.py

@@ -49,7 +49,7 @@ try:
     # 0.98, and the second will fail for 0.98.0
     EnsureSConsVersion(0, 98)
     EnsureSConsVersion(0, 98, 1)
-except SystemExit, e:
+except SystemExit as e:
     print("""
 For more details, see:
     http://gem5.org/Dependencies
@@ -59,7 +59,7 @@ For more details, see:
 # pybind11 requires python 2.7
 try:
     EnsurePythonVersion(2, 7)
-except SystemExit, e:
+except SystemExit as e:
     print ("""
 You can use a non-default installation of the Python interpreter by
 rearranging your PATH so that scons finds the non-default 'python' and

site_scons/site_tools/default.py

@@ -61,7 +61,7 @@ def common_config(env):
         "M5",              # M5 configuration (e.g., path to kernels)
         ]
 
-    for key,val in sorted(os.environ.iteritems()):
+    for key,val in sorted(os.environ.items()):
         if key in use_vars or \
                 any([key.startswith(prefix) for prefix in use_prefixes]):
             env['ENV'][key] = val

site_scons/site_tools/git.py

@@ -54,7 +54,7 @@ def install_style_hooks(env):
     try:
         gitdir = env.Dir(readCommand(
             ["git", "rev-parse", "--git-dir"]).strip("\n"))
-    except Exception, e:
+    except Exception as e:
         print("Warning: Failed to find git repo directory: %s" % e)
         return