systemc: Hook up sc_main.

systemc: Hook up sc_main.

sc_main is exported as a python method on the SystemC_Kernel class and
takes a series of string arguments. The internal c++ implementation
converts those arguments into the standard argc and argv and uses them
to call the standard SystemC version of that function.

A weak SystemC version of sc_main is provided so that systemc will
compile with or without a simulation provided version of that
function. The weak version just complains and dies.

Change-Id: Iad735536c37c8bc85d06cf24779f607ae4309b8b
Reviewed-on: https://gem5-review.googlesource.com/10824
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>