[analyzer] Fully-covered switch for families in isTrackedFamily()
MachineScheduler: format DEBUG output.

I'm getting more serious about tuning and enabling on x86/ARM. Start
by making the trace readable.
Disable DFSResult for ConvergingScheduler.

For now, just save the compile time since the ConvergingScheduler
heuristics don't use this analysis. We'll probably enable it later
after compile-time investigation.
RegisterPressure heuristics currently require signed comparisons.