* som.c (som_misc_symbol_info): Add field

    * som.c (som_misc_symbol_info):  Add field
        secondary_def.
        (som_bfd_derive_misc_symbol_info):  Initialize
        secondary_def.
        (som_build_and_write_symbol_table): Keep track
        of secondary_def field.
        (som_slurp_symbol_table): Set BSF_WEAK symbol flag
        if secondary_def field is set.
        (som_bfd_ar_write_symbol_stuff): Initialize
        secondary_def.