Add weak symbols as an extension to a.out.

	Add weak symbols as an extension to a.out.
	* aoutx.h (sym_in_text_section): Don't define.
	(sym_in_data_section, sym_in_bss_section): Likewise.
	(sym_is_undefined, sym_is_global_defn): Likewise.
	(sym_is_debugger_info, sym_is_fortrancommon): Likewise.
	(sym_is_absolute, sym_is_indirect): Likewise.
	(translate_from_native_sym_flags): Rewrite for clarity.  Rearrange
	arguments and change caller.  Handle weak symbols.
	(translate_to_native_sym_flags): Likewise.
	(aout_link_check_ar_symbols): Don't ignore weak symbols.  Pull
	object in from archive if a weak defintion is found for an
	existing undefined symbol.
	(aout_link_add_symbols): Put all cases in switch.  Set flags of an
	undefined symbol to 0.  Handle weak symbols.
	(aout_link_write_symbols): Handle weak symbols.
	(aout_link_write_other_symbol): Likewise.
	(aout_link_input_section_std): Likewise.
	(aout_link_input_section_ext): Likewise.
	* sunos.c (sunos_write_dynamic_symbol): Likewise.