Turn dead-code removal back on when not simulavr
datalog: add a tip showing gnuplot usage

Add a comment to the datalog output showing how it can be viewed with
gnuplot.  It would be trivial to add this as a .plot script, but it's
even easier in the datalog output.
simulator: Make time-scale=0 a cmdline option

Teach the simulator to run with no delays when time-scale=0.

Let the user specify the time-scale on the command line.