MacOS stack traces use the already mmapped executable

...rather than trying to find the executable on the file system.

Also use a more robust PIE offset calculation based on the
available metadata.

And for the last function, use the data that tells the end
rather than assuming 4K.

Also they print in a consistent way with Linux stack traces.
5c1ec20c9aAndrew Kelley committed on 8/23/2018, 8:23:33 PMparent8f96553
4 files changedLine totals unavailable