Fix non-deterministic behavior when generating MIPS GOT.

Fix non-deterministic behavior when generating MIPS GOT.

	* mips.cc (Mips_got_entry::Mips_got_entry): Remove object argument
	for global got symbols, and set addend to 0.
	(Mips_got_entry::hash): Change hash algorithm.
	(Mips_got_entry::equals): Refactor.
	(Mips_got_entry::object): Return input object for local got symbols
	from union d.
	(Mips_got_entry::addend): Change return of the relocation addend.
	(Mips_got_entry::addend_): Move from union d.
	(Mips_got_entry::object_): Move into union d.
	(class Mips_symbol_hash): New class.
	(Mips_got_info::Global_got_entry_set): New type.
	(Mips_got_info::global_got_symbols): Change return type to
	Global_got_entry_set.
	(Mips_got_info::global_got_symbols_): Change type to
	Global_got_entry_set.
	(Mips_symbol::hash): New method.
	(Mips_output_data_la25_stub::symbols_): Change type to std::vector.
	(Mips_output_data_mips_stubs::Mips_stubs_entry_set): New type.
	(Mips_output_data_mips_stubs::symbols_): Change type to
	Mips_stubs_entry_set.
	(Mips_got_info::record_global_got_symbol): Don't pass object
	argument when creating global got symbol.
	(Mips_got_info::record_got_entry): Remove find before inserting
	got entries.
	(Mips_got_info::add_reloc_only_entries): Change type of iterator
	to Global_got_entry_set.
	(Mips_got_info::count_got_symbols): Likewise.
	(Mips_output_data_la25_stub::create_la25_stub): Use push_back
	for adding entries to symbols_.
	(Mips_output_data_la25_stub::do_write): Change type of iterator
	to std::vector.
	(Mips_output_data_mips_stubs::set_lazy_stub_offsets): Change type
	of iterator to Mips_stubs_entry_set.
	(Mips_output_data_mips_stubs::set_needs_dynsym_value): Likewise.
	(Mips_output_data_mips_stubs::do_write): Likewise.