systemc: Only build python utility code if python is enabled.

Change-Id: I58054ddd0d5ef0dbee18028c4218e7418347f959
Reviewed-on: https://gem5-review.googlesource.com/c/13979
Maintainer: Gabe Black <gabeblack@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

src/systemc/core/SConscript

@@ -38,7 +38,6 @@ if env['USE_SYSTEMC']:
     Source('object.cc')
     Source('port.cc')
     Source('process.cc')
-    Source('python.cc')
     Source('scheduler.cc')
     Source('sched_event.cc')
     Source('sensitivity.cc')
@@ -63,4 +62,5 @@ if env['USE_SYSTEMC']:
     Source('sc_time.cc')
 
     if env['USE_PYTHON']:
+        Source('python.cc')
         Source('sc_main_python.cc')