[crdavidson]

So, dtrace2spall is going to generate much smaller files and impact runtime less, because it samples with dtrace, and then converts the data to spall's format as a post-pass.

Auto-tracing is far more comprehensive, but it's a big datadump, and it does impact runtimes a bit more.

So far I've mostly used auto-tracing to figure out how bigger pieces of code work, rather than strictly for profiling. It was super helpful trying to walk through the more complicated parts of the Odin compiler to fix things, being able to see the order of functions called on the timeline.