* object.cc (Sized_relobj::include_section_group): Adjust section

	* object.cc (Sized_relobj::include_section_group): Adjust section
	indexes read from group data.  Build vector to pass to
	layout_group.
	* layout.cc (Layout::layout_group): Add flags and shndxes
	parameters.  Remove contents parameter.  Change caller.  Update
	explicit instantiations.
	* layout.h (class Layout): Update layout_group declaration.
	* output.cc (Output_data_group::Output_data_group): Add flags and
	input_shndxes parameters.  Remove contents parameter.  Change
	caller.
	(Output_data_group::do_write): Change input_sections_ to
	input_shndxes_.
	* output.h (class Output_data_group): Update constructor
	declaration.  Rename input_sections_ to input_shndxes_.
	* testsuite/many_sections_test.cc: Add template.