By ignoring SIG_TRAP, using --debug-break <N> when not connected to
a debugger becomes a no-op. Apparently this was intended to be a
feature, though the rationale is not clear.
If we don't ignore SIG_TRAP, then using --debug-break <N> when not
connected to a debugger causes the simulation process to terminate
at tick N. This is occasionally useful, e.g., if you just want to
collect a trace for a specific window of execution then you can combine
this with --debug-start to do exactly that.
In addition to not ignoring the signal, this patch also updates
the --debug-break help message and deletes a handful of unprotected
calls to Debug::breakpoint() that relied on the prior behavior.
28a0e5a165