Change Section_id type to use Relobj* instead of Object*.

Change Section_id type to use Relobj* instead of Object*.

2015-04-29  Cary Coutant  <cary@google.com>
	    Rafael Ávila de Espíndola <rafael.espindola@gmail.com>

gold/
	* gc.h (Garbage_collection::is_section_garbage): Change Object*
	to Relobj*.
	(Garbage_collection::add_reference): Likewise.
	(Garbage_collection::gc_process_relocs): Likewise. Don't push
	object/shndx pair onto *secvec for dynamic objects. Don't follow
	relocations pointing to dynamic objects for GC.
	* icf.cc (Icf::find_identical_sections): Change Object* to Relobj*.
	(Icf::unfold_section): Likewise.
	(Icf::is_section_folded): Likewise.
	(Icf::get_folded_section): Likewise.
	* icf.h: (Icf::get_folded_section): Likewise.
	(Icf::unfold_section): Likewise.
	(Icf::is_section_folded): Likewise.
	(Icf::section_has_function_pointers): Likewise.
	(Icf::set_section_has_function_pointers): Likewise.
	* object.h (Section_id): Likewise.
	(Const_section_id): Likewise.
	* output.cc (Output_section::update_section_layout): Likewise.
	* output.h: (Output_section_lookup_maps::find_relaxed_input_section):
	Likewise.
	* plugin.cc (update_section_order): Likewise.
	(unique_segment_for_sections): Likewise.
	* powerpc.cc (Powerpc_relobj::add_reference): Likewise.
	(Target_powerpc::do_gc_add_reference): Likewise.
	(Target_powerpc::gc_process_relocs): Likewise.
	(Target_powerpc::do_gc_add_reference): Likewise.
	* symtab.cc (Symbol_table::is_section_folded): Likewise.
	(Symbol_table::gc_mark_symbol): Likewise.
	* symtab.h: (Symbol_table::is_section_folded): Likewise.
	* target.h: (Sized_target::gc_add_reference): Likewise.
	(Sized_target::do_gc_add_reference): Likewise.