Support 'info proc' for FreeBSD process core dumps.
- Command line arguments are obtained from the pr_psargs[] array
saved in the NT_PRPSINFO note.
- The 'cwd' and 'exe' values are obtained from the per-process file
descriptor table stored in the NT_PROCSTAT_FILES core note.
- 'mappings' is implemented by walking the array of VM map entries
stored in the NT_PROCSTAT_VMMAP core note.
- 'status' output is generated by outputting fields from
the first structure stored in the NT_PROCSTAT_PROC core note.
- 'stat' is aliased to 'status'.