systemc: Fix systemc array bound error

systemc: Fix systemc array bound error

Currently, gcc 10.0 does not compile gem5 due to an array bound error
in sc_unsigned and sc_signed constructors.

Previous fix only ignores array-bounds warnings for sc_unsigned.cc and
sc_signed for gcc 10.1 onwards.

This commit turns the ignoring array-bounds warning flag on for all
gcc 10 onwards.

JIRA: https://gem5.atlassian.net/browse/GEM5-677.

Change-Id: Id65b6d52cef527f62917e09231ff79e2237affd8
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31634
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>