common.opt (gdwarf-): Initialize dwarf_version to -1 instead of 2.

common.opt (gdwarf-): Initialize dwarf_version to -1 instead of 2.

        * common.opt (gdwarf-): Initialize dwarf_version to -1 instead of 2.
        * toplev.c (process_options): Default to dwarf_version 2.
        * config/vxworks.c (vxworks_override_options): Default to strict-dwarf
        and dwarf_version 2.

From-SVN: r186783