elf_backend_section_flags and _bfd_elf_init_private_section_data

elf_backend_section_flags and _bfd_elf_init_private_section_data

I was looking at elf_backend_section_flags as a means of setting
SEC_SMALL_DATA for .sdata, .sbss and the like, and condidered adding
an asection* parameter to access the section name easily before
realising that hdr->bfd_section of course makes the section
available.  So no new parameter needed.  In fact the flagword*
parameter isn't needed either, so out it goes.

The patch also tidies some horrible code in _bfd_elf_new_section_hook
that can change whether known ABI sections have sh_type and sh_flags
set up depending on which of the bfd_make_section functions is used.
(Some of those set section flags before _bfd_elf_new_section_hook is
called, others leave the flags zero.)  The function also had some
hacks for .init_array and .fini_array to affect how
_bfd_elf_init_private_section_data behaved for those sections.  It's
cleaner to do that in _bfd_elf_init_private_section_data.  So that all
goes and we now init sh_type and sh_flags for all known ABI sections
in _bfd_elf_new_section_hook.  _bfd_elf_init_private_section_data is
changed to suit, and now doesn't just single out SHT_INIT_ARRAY and
SHT_FINI_ARRAY but rather any of the special section types.

The _bfd_elf_new_section_hook change resulting in
+FAIL: ld-aarch64/erratum835769-843419
exposing some errors in the aarch64 backend.  elfNN_aarch64_size_stubs
should not be looking at linker created sections in the stub bfd.  Nor
should code like "symtab_hdr = &elf_tdata (input_bfd)->symtab_hdr" be
run without first checking that input_bfd is ELF.

	* elf-bfd.h (elf_backend_section_flags): Remove flagword* param.
	* elf.c (_bfd_elf_make_section_from_shdr): Set section flags before
	calling elf_backend_section_flags with adjusted params.  Use
	newsect->flags past that point.
	(_bfd_elf_new_section_hook): Always set sh_type and sh_flags for
	special sections.
	(_bfd_elf_init_private_section_data): Allow normal sh_type sections
	to have their type overridden, and all sh_flags but processor and
	os specific.
	* elf32-arm.c (elf32_arm_section_flags): Adjust for changed params.
	* elf32-mep.c (mep_elf_section_flags): Likewise.
	* elf32-nios2.c (nios2_elf32_section_flags): Likewise.
	* elf64-alpha.c (elf64_alpha_section_flags): Likewise.
	* elf64-ia64-vms.c (elf64_ia64_section_flags): Likewise.
	* elfnn-ia64.c (elfNN_ia64_section_flags): Likewise.
	* elfnn-aarch64.c (elfNN_aarch64_size_stubs): Exclude the linker
	stub BFD and non-aarch64 input files when scanning for stubs.