* target.h (Target::gc_mark_symbol, do_gc_mark_symbol): New functions.

	* target.h (Target::gc_mark_symbol, do_gc_mark_symbol): New functions.
	(Sized_target::gc_add_reference, do_gc_add_reference): New functions.
	* gc.h (gc_process_relocs): Call target gc_add_reference.
	* gold.cc (queue_middle_tasks): Use gc_mark_symbol on start sym.
	* symtab.cc (Symbol_table::gc_mark_undef_symbols): Use gc_mark_symbol.
	(Symbol_table::gc_mark_symbol): Call target gc_mark_symbol. Remove
	unnecessary cast.
	* powerpc.cc (Powerpc_relobj::get_opd_ent): Rearrange parameters
	to cater for when we don't need code offset.  Update use.
	(Powerpc_relobj::access_from_map_, opd_valid_): New vars.
	(Powerpc_relobj::access_from_map, add_reference, opd_valid,
	set_opd_valid): New functions.
	(Target_powerpc::do_gc_add_reference): New function.
	(Target_powerpc::gc_process_relocs): Call gc()->add_reference on
	stashed refs.
	(Target_powerpc::do_gc_mark_symbol): New function.