* config/arc/arc.opt: Update optin names, replacing '_' hyphenation
        with '-' hypphenation.
        * config/arc/arc.h (CPP_SPEC): Likewise.
        (ASM_SPEC): Likewise.
        Remove invalid / SELF_SPEC translated option alternatives.
        (DRIVER_SPELF_SPECS): Use option alternatives for mARC5|mA5 and
        mav2em|mARCv2EM|mEM .
        Also remove from processed options mARC5/mA7/ARCv2EM/mEM .
        Add backwards compatibility translations from '_' hypenated options
        to '-' hyphenated options.