Run eh_frame optimisation for relocatable link

Run eh_frame optimisation for relocatable link

The idea here is to drop .eh_frame FDEs corresponding to dropped
comdat group sections or linkonce sections, but not perform changes in
encoding.

bfd/
	PR 17467
	* elf-eh-frame.c (ENSURE_NO_RELOCS): Don't stop at first NONE reloc.
	(_bfd_elf_parse_eh_frame): When relocatable output, don't set
	flags enabling conversion of CIEs and FDEs to use relative encoding.
	(find_merged_cie): Similarly.
	(_bfd_elf_write_section_eh_frame): Don't edit FDEs when
	relocatable, except for CIE pointer.
	* elflink.c (bfd_elf_reloc_symbol_deleted_p): Return true for
	relocs against symbols in dropped comdat group sections.
	(bfd_elf_discard_info): Do some eh_frame optimisation when
	relocatable.
ld/
	* ldlang.c (lang_add_section): Set up map_head.s and map_tail.s when
	relocatable.