scons: Use six.input instead of raw_input.

raw_input is not defined in python 3.x and has been replaced by "input".
The "six" compatiblity module defines its own "input" method which
figures out which to use under the covers.

Change-Id: I13a885dd45ec0160c7b46e334b06aae239e3c836
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27948
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

site_scons/site_tools/git.py

@@ -44,6 +44,7 @@ import sys
 
 import gem5_scons.util
 from m5.util import readCommand
+from six.moves import input
 
 git_style_message = """
 You're missing the gem5 style or commit message hook. These hooks help
@@ -102,7 +103,7 @@ def install_style_hooks(env):
 
     print(git_style_message, end=' ')
     try:
-        raw_input()
+        input()
     except:
         print("Input exception, exiting scons.\n")
         sys.exit(1)