* output.h (Output_data_dynamic::add_section_size): New method

	that takes two Output_data objects.
	(Output_data_dynamic::Dynamic_entry): Create storage for secondary
	entry param.  Handle it in initializers.
	* output.cc (Output_data_dynamic::Dynamic_entry::write): For
	DYNAMIC_SECTION_SIZE, add in second object size if non-NULL.
	* layout.h (Layout::add_target_dynamic_tags): Add dynrel_includes_plt
	arg.
	* layout.cc (Layout::add_target_dynamic_tags): If dynrel_includes_plt,
	and .rela.plt exists, set DT_REL{,A}SZ to sum of .rela.dyn and .rela.plt
	* arm.cc (Target_arm::do_finalize_sections): Update to pass false
	for dynrel_includes_plt.
	* i386.cc (Target_i386::do_finalize_sections): Likewise.
	* x86_64.cc (Target_x86_64::do_finalize_sections): Likewise.
	* sparc.cc (Target_sparc::make_plt_entry): Force .rela.dyn to be output
	before .rela.plt
	(Target_sparc::do_finalize_sections): Update to pass true for
	dynrel_includes_plt.
	* powerpc.cc (Target_powerpc::make_plt_entry): Force .rela.dyn to be
	output before .rela.plt
	(Target_powerpc::do_finalize_sections): Update to pass true for
	dynrel_includes_plt when 32-bit.