Some clients (e.g. fastmodel integration) would like to catch specific warning messages from SystemC. Adding facilities to chain extra report handler (instead of just replacing the default one), that are run after the default/set handler. Change-Id: I8ef140fc897ae5eee0fc78c70caf081f625efbfd Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/67234 Reviewed-by: Gabe Black <gabe.black@gmail.com> Maintainer: Gabe Black <gabe.black@gmail.com> Tested-by: kokoro <noreply+kokoro@google.com>