Include the main C++ file only with Verilator
Include the main C++ file only with Verilator

This is necessary for having VCS support with simple system example.
Because in the ibex_simple_system_main.cc we are including some
Verilator exclusive header files.

Signed-off-by: Canberk Topal <e6b05429a51cc3258c31cb1f7836595b60921a29@lowrisc.org>

lowRISC/ibex,lowRISC/ibex,AmbiML/ibex,AmbiML/ibex,lowRISC/ibex,AmbiML/ibex,lowRISC/ibex,AmbiML/ibex