Support .gnu.lto_.lto section in ELF files (PR 24768).

Support .gnu.lto_.lto section in ELF files (PR 24768).

bfd/ChangeLog:

2019-07-22  Martin Liska  <mliska@suse.cz>

	PR 24768
	* archive.c (_bfd_compute_and_write_armap): Come up with
	report_plugin_err variable.
	* bfd-in2.h (struct bfd): Add lto_slim_object flag.
	* elf.c (struct lto_section): New.
	(_bfd_elf_make_section_from_shdr): Parse content of
	.gnu_lto_.lto section.
	* elflink.c: Report error for a missing LTO plugin.
	* linker.c (_bfd_generic_link_add_one_symbol): Likewise.

binutils/ChangeLog:

2019-07-22  Martin Liska  <mliska@suse.cz>

	PR 24768
	* nm.c (filter_symbols): Set report_plugin_err if
	error is reported.
	(display_rel_file): Report error for a missing LTO plugin.

gold/ChangeLog:

2019-07-22  Martin Liska  <mliska@suse.cz>

	PR 24768
	* layout.h (class Layout): Add is_lto_slim_object and
	set_lto_slim_object.
	* object.cc (struct lto_section): Add lto_slim_object_.
	(big_endian>::do_layout): Parse content of
	.gnu_lto_.lto section.
	(big_endian>::do_add_symbols): Report error for a missing
	LTO plugin.