scons: Switch from the print statement to the print function.

Starting with version 3, scons imposes using the print function instead
of the print statement in code it processes. To get things building
again, this change moves all python code within gem5 to use the
function version. Another change by another author separately made this
same change to the site_tools and site_init.py files.

Change-Id: I2de7dc3b1be756baad6f60574c47c8b7e80ea3b0
Reviewed-on: https://gem5-review.googlesource.com/8761
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

ext/libelf/SConscript

@@ -28,6 +28,8 @@
 #
 # Authors: Nathan Binkert
 
+from __future__ import print_function
+
 import os, subprocess
 
 Import('main')
@@ -114,8 +116,8 @@ if m4env.Detect('gm4'):
 # Check that m4 is available
 import SCons.Tool.m4
 if not SCons.Tool.m4.exists(m4env):
-   print "Error: Can't find version of M4 macro processor.  " + \
-         "Please install M4 and try again."
+   print("Error: Can't find version of M4 macro processor.  " +
+         "Please install M4 and try again.")
    Exit(1)
 
 m4env.Append(M4FLAGS=['-DSRCDIR=%s' % Dir('.').path])