Delete relocations associatesd with deleted exidx entries.

Delete relocations associatesd with deleted exidx entries.

	PR ld/20595
ld	* testsuite/ld-arm/unwind-4.d: Add -q option to linker command
	line and -r option to objdump command line.  Match emitted relocs
	to make sure that superflous relocs are not generated.

bfd	* elf-bfd.h (struct elf_backend_data): Add
	elf_backend_count_output_relocs callback to count relocations in
	the final output.
	* elf-arm.c (elf32_arm_add_relocation): Deleted.
	(elf32_arm_write_section): Move additional relocation to emit_relocs.
	(elf32_arm_count_output_relocs): New function.
	(emit_relocs): New function.
	(elf32_arm_emit_relocs): New function.
	(elf32_arm_vxworks_emit_relocs): New function.
	(elf_backend_emit_relocs): Updated to use the new functions.
	(elf_backend_count_output_relocs): New define.
	* bfd/elflink.c (bfd_elf_final_link): Do not add additional_reloc_count
	to the relocation count.
	(_bfd_elf_link_size_reloc_section): Use callback to count the
	relocations which will be in output.
	(_bfd_elf_default_count_output_relocs): New function.
	* bfd/elfxx-target.h (elf_backend_count_output_relocs): New define.