scons: Import "sys" which is used in an exception handler.

If the call to "raw_input" fails (it does in python 3.x), then the
"except" runs and will also fail because sys hasn't been imported.

Change-Id: Ibf5778a893a5bd8aad17f4aee544ddcfe5085cab
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27947
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed