[GOLD] Got_offset_list: addend field

[GOLD] Got_offset_list: addend field

This is the first in a series of patches aimed at supporting GOT
entries against symbol plus addend generally for PowerPC64 rather than
just section symbol plus addend as gold has currently.

This patch adds an addend field to Got_offset_list, so that both local
and global symbols can have GOT entries with addend.

	PR 28192
	* object.h (Got_offset_list): Add addend_ field, init in both
	constructors.  Adjust all accessors to suit.
	(Sized_relobj::do_local_has_got_offset): Adjust to suit.
	(Sized_relobj::do_local_got_offset): Likewise.
	(Sized_relobj::do_set_local_got_offset): Likewise.
	* symtab.h (Symbol::has_got_offset): Add optional addend param.
	(Symbol::got_offset, Symbol::set_got_offset): Likewise.
	* incremental.cc (Local_got_offset_visitor::visit): Add unused
	uint64_t parameter with FIXME.
	(Global_got_offset_visitor::visit): Add unused uint64_t parameter.