Pass section when available to bfd_octets_per_byte

Pass section when available to bfd_octets_per_byte

and other tidies.  I think it's better to default to passing the
section to bfd_octets_per_byte, even in cases where we know it won't
make a difference.

A number of the coff reloc functions used bfd_octets_per_byte wrongly,
not factoring it into the offset into the data buffer.  As it happens,
the targets using those files always had bfd_octets_per_byte equal to
one, so there wasn't any detectable wrong behaviour.  However, it is
wrong in the source and might cause trouble for anyone creating a new
target.  Besides fixing that, the patch also defines OCTETS_PER_BYTE
as one in target files where that is appropriate.

bfd/
	* archures.c (bfd_octets_per_byte): Tail call
	bfd_arch_mach_octets_per_byte.
	* coff-arm.c (OCTETS_PER_BYTE): Define.
	(coff_arm_reloc): Introduce new "octets" temp.  Use OCTETS_PER_BYTE
	with section.  Correct "addr".  Remove ATTRIBUTE_UNUSED.
	* coff-i386.c (coff_i386_reloc): Similarly.
	* coff-mips.c (mips_reflo_reloc): Similarly.
	* coff-x86_64.c (coff_amd64_reloc): Similarly.
	* elf32-msp430.c (OCTETS_PER_BYTE): Define.
	(rl78_sym_diff_handler): Use OCTETS_PER_BYTE, with section.
	* elf32-nds32.c (nds32_elf_get_relocated_section_contents): Similarly.
	* elf32-ppc.c (ppc_elf_addr16_ha_reloc): Similarly.
	* elf32-pru.c (pru_elf32_do_ldi32_relocate): Similarly.
	* elf32-s12z.c (opru18_reloc): Similarly.
	* elf32-sh.c (sh_elf_reloc): Similarly.
	* elf32-spu.c (spu_elf_rel9): Similarly.
	* elf32-xtensa.c (bfd_elf_xtensa_reloc): Similarly.
	* elf64-ppc.c (ppc64_elf_ha_reloc, ppc64_elf_brtaken_reloc),
	(ppc64_elf_toc64_reloc): Similarly.
	* bfd.c (bfd_get_section_limit): Pass section to bfd_octets_per_byte.
	* cofflink.c (_bfd_coff_link_input_bfd),
	(_bfd_coff_reloc_link_order): Likewise.
	* elf.c (_bfd_elf_section_offset): Likewise.
	* elflink.c (resolve_section, bfd_elf_perform_complex_relocation),
	(elf_link_input_bfd, elf_reloc_link_order, elf_fixup_link_order),
	(bfd_elf_final_link): Likewise.
	* elf.c (_bfd_elf_make_section_from_shdr): Don't strncmp twice
	to set SEC_ELF_OCTETS.
	* reloc.c (bfd_perform_relocation): Tidy SEC_ELF_OCTETS special case.
	(bfd_install_relocation): Likewise.
	(_bfd_final_link_relocate): Don't recalculate octets.
	* syms.c (_bfd_stab_section_find_nearest_line): Introduc new
	"octets" temp.
	* bfd-in2.h: Regenerate.
ld/
	* ldexp.c (fold_name): Pass section to bfd_octets_per_byte.
	* ldlang.c (init_opb): Don't call bfd_arch_mach_octets_per_byte
	unnecessarily.