systemc: Modify reportifyException to keep sc_reports in scope.

systemc: Modify reportifyException to keep sc_reports in scope.

reportifyException was sometimes indirectly creating temporary
sc_report objects which would go out of scope when they were
returned. The later code which tried to print them would then read
garbage.

Change-Id: I0a744eb029c62bf2ffee83db0a0e6dcbe3e60f7d
Reviewed-on: https://gem5-review.googlesource.com/c/13190
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>