systemc: Use the "catch action" and the handler func outside sc_main.

systemc: Use the "catch action" and the handler func outside sc_main.

If an exception escapes sc_main, Accellera catches it and feeds it
into the report handler, telling it to run the catch actions. This
seems like it sets up lots of dangerous scenarios, and also makes a
vital error detecting path more complex and error prone.

On the other hand, it makes one of the tests pass.

Change-Id: I7f9d07e01e63c7abeee903febe2e434041ec49a4
Reviewed-on: https://gem5-review.googlesource.com/c/13307
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>