Add a wrapper script to run a simple_system binary under Spike
Add a wrapper script to run a simple_system binary under Spike

The main point of this is that it's somewhere we can store what it
calls "ss_opts": the options that we must pass to Spike to tell it the
memory layout of the simple_system environment.

While we're at it, I've tried to make this reasonably pleasant to use.
So you can do

   spike-simple-system.sh <elf-file>

just to run the thing. To pass stuff to Spike without the
bash script getting in the way, use '--':

   spike-simple-system.sh -- my option -h --here <elf-file>

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