gem5: update to 4c8efdbef45d98109769cf675ee3411393e8ed06

The Linux boot was still broken after the previous gem5 update. Let's try
a new one...

Add the --no-ccache option to benchmark builds.

common.py

@@ -221,6 +221,13 @@ CPU architecture to use. If given multiple times, run the action
 for each arch sequentially in that order. If one of them fails, stop running.
 Valid archs: {}
 '''.format(arches_string)
+        )
+        self.add_argument(
+            '--ccache',
+            default=True,
+            help='''\
+Enable or disable ccache: https://cirosantilli.com/linux-kernel-module-cheat#ccache
+'''
         )
         self.add_argument(
             '--dry-run',