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: Revamp the systemc SConscripts.

The existing scripts were including pthread code and QT code at the same
time, and also insisting on an having a set of architecture specific
source files for whatever the current architecture is.

This change selects using either QT or pthreads based on the host
architecture, distributes accumulating source files, list source files
explicitly (to avoid including redundant coroutine libraries) and makes
scons insist on an architecture specific QT implementation only if QT is
being used. It also defines a preprocessor symbol which tells some headers
whether or not pthreads are being used, and also clones the scons
environment to avoid leaking flags into the main environment used to
compile gem5 itself.

If the host architecture isn't supported by systemc, a warning will be
printed, and the various build products and SConscript files will be
skipped over.

Change-Id: I1a40123a11e49e02922a054f093246cf197087bf
Reviewed-on: https://gem5-review.googlesource.com/3461
Reviewed-by: Matthias Jung <jungma@eit.uni-kl.de>
Reviewed-by: Christian Menard <christian.menard@tu-dresden.de>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>