Packaging: Restrict 7zip to 2 threads

Otherwise can create out-of-memory situations on 32bit machines
with many cores.

Change-Id: I7cc862d30079ff0fb11a3c088ae38d73afce4b1e
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

scripts/createDistPackage.py

@@ -58,7 +58,7 @@ def main():
             common.codesign(tempdir)
         # package
         zip_source = os.path.join(tempdir, '*') if arguments.exclude_toplevel else tempdir
-        subprocess.check_call([arguments.sevenzip, 'a',
+        subprocess.check_call([arguments.sevenzip, 'a', '-mmt2',
             arguments.target_archive, zip_source])
     finally:
         shutil.rmtree(tempdir_base)