Fix issue where first reserved word of GOT is not initialized if there
is no PLT.

gold/
	PR gold/16900
	* i386.cc (Output_data_got_plt_i386): New class.
	(Output_data_plt_i386::Output_data_plt_i386): Change type of got_plt
	parameter. Change all callers.
	(Output_data_plt_i386::layout_): Remove.
	(Output_data_plt_i386::got_plt_): Change type.
	(Target_i386::got_plt_): Change type. Change all references.
	(Target_i386::got_section): Create instance of new class.
	(Output_data_got_plt_i386::do_write): New function.
	* x86_64.cc (Output_data_got_plt_x86_64): New class.
	(Output_data_plt_x86_64::Output_data_plt_x86_64): Change type of got_plt
	parameter. Change all callers.
	(Output_data_plt_x86_64::layout_): Remove.
	(Output_data_plt_x86_64::got_plt_): Change type.
	(Target_x86_64::got_plt_): Change type. Change all references.
	(Target_x86_64::got_section): Create instance of new class.
	(Output_data_got_plt_x86_64::do_write): New function.
	(Output_data_plt_x86_64::do_write): Don't write reserved words in GOT.
	(Target_x86_64<size>::init_got_plt_for_update): Create instance of new
	class.