Don't read and cache local syms for gc-sections

Don't read and cache local syms for gc-sections

Most places just need the local sym section, so reading and sometimes
caching the symbols is excessive.  A symbol shndx can be stored in 4
bytes, an elf symbol internal form requires 32 bytes.  When caching
the local symbols we went slightly crazy trying to avoid memory usage,
resulting in the symbols being freed then immediately read again for
the testcase in the PR33530.

To avoid this problem, this patch caches the local symbol section
indices in the bfd rather than in the reloc cookie.  They are not
initialised until there is a need for them, so unlike elf_sym_hashes
for global syms you cannot rely on them being present.

One place that does need local syms is adjust_eh_frame_local_symbols,
but that is called once via bfd_discard_info so there is no problem
simply reading them.  The other place that needs local syms is
ppc64_elf_gc_mark_hook for the old ELFv1 ABI when handling .opd.
bfd_sym_from_r_symndx should be sufficient for function pointer
references to static functions, which is how this code is triggered.

	PR 33530
	* elf-bfd.h (struct elf_reloc_cookie): Delete "locsyms",
	"sym_hashes", "bad_symtab".  Make "locsymcount" and
	"extsymoff" unsigned int.
	(struct elf_obj_tdata): Add loc_shndx.
	(elf_loc_shndx): Define.
	(_bfd_get_local_sym_section): Declare.
	* elf-eh-frame.c (find_merged_cie): Use
	_bfd_get_local_sym_section for local syms.
	(adjust_eh_frame_local_symbols): Read local syms if any match
	.eh_frame section.  Return them if changed.
	(_bfd_elf_discard_section_eh_frame): Adjust.
	* elf64-ppc.c (ppc64_elf_gc_mark_hook): Use
	_bfd_get_local_sym_section.  Use bfd_sym_from_r_symndx when
	reading opd local symbol.
	* elflink.c (_bfd_get_local_sym_section): New function.
	(_bfd_elf_section_for_symbol): Use it.
	(elf_link_add_object_symbols): Remove unnecessary cast on
	bfd_zalloc return.
	(init_reloc_cookie): Remove "info" and "keep_memory" params.
	Adjust all callers.  Don't stash elf_sym_hashes and
	elf_bad_symtab to cookie.  Don't read local syms to cookie.
	(fini_reloc_cookie): Do nothing.
	(_bfd_elf_gc_mark_hook): Use _bfd_get_local_sym_section.
	(elf_gc_mark_debug_section): Likewise.
	(bfd_elf_reloc_symbol_deleted_p): Likewise.  Update cookie use.