Don't attach linker created section to --just-syms bfd

Don't attach linker created section to --just-syms bfd

All sections on a --just-syms bfd are discarded from the output, so
attaching linker created sections to such a bfd results in errors.
In other cases, like the .note.GNU-stack check, it's wrong to have a
--just-syms object potentially affect the output.

bfd/
	* elflink.c (_bfd_elf_link_create_dynstrtab): Don't make dynobj
	a --just-syms bfd.
	(_bfd_elf_size_group_sections): Skip --just-syms bfds.
	(bfd_elf_size_dynamic_sections): Ignore .note.GNU-stack and
	.preinit_array on --just-syms bfds.
	(_bfd_elf_gc_mark_extra_sections): Skip --just-syms bfds.
	(elf_gc_sweep, bfd_elf_parse_eh_frame_entries): Likewise.
	(bfd_elf_gc_sections, bfd_elf_discard_info): Likewise.
ld/
	* emultempl/elf32.em (gld${EMULATION_NAME}_after_open): Skip
	--just-syms bfds when looking for a place to attach .note.gnu.build-id
	and .eh_frame_hdr sections.  Delete dead code.