backends: Add ebl_check_reloc_target_type.

And implement for arm and ia64. Both have special section types that
are valid targets for a reloc. Both refer to unwind data. elflint now
just calls ebl_check_reloc_target_type instead of hard coding the
expected section types.

Signed-off-by: Mark Wielaard <mjw@redhat.com>
13 files changed