may_use_rel_p, may_use_rela_p, default_use_rela_p.
(bfd_elf_section_data): Add use_rela_p.
* elf.c (bfd_section_from_shdr): Set use_rela_p appropriately.
(_bfd_elf_new_section_hook): Likewise.
(elf_fake_sections): Use may_use_rela_p, etc., instead of
use_rela_p.
(_bfd_elf_copy_private_section_data): Copy use_rela_p.
* elfcode.h (write_relocs): Determine whether or not use rela
relocs based on the relocation section header.
* elflink.c (_bfd_elf_create_dynamic_sections): Use default_use_rela_p
instead of use_rela_p.
* elfxx-target.h (elf_backend_may_use_relp): New macro.
(elf_backend_may_use_rela_p): Likewise.
(elf_backend_default_use_rela_p): Likewise.
(elfNN_bed): Use them.
