* elf-bfd.h (struct elf_backend_data): Add got_ & plt_header_size.

    * elf-bfd.h (struct elf_backend_data): Add got_ & plt_header_size.
        * elf32-i386.c (elf_backend_got_header_size): Define.
        (elf_backend_plt_header_size): Define.
        * elf32-m68k.c, elf32-mips.c, elf32-ppc.c: Likewise.
        * elf32-sparc.c, elf64-alpha.c, elf64-sparc.c: Likewise.
        * elfxx-target.h: Provide a default of zero.
        * elflink.c (_bfd_elf_create_got_section): Use got_header_size.
        * elflink.h (elf_gc_common_finalize_got_offsets): Likewise.

        * elf32-ppc.c (ppc_elf_adjust_dynamic_symbol): Don't remove a PLT
        entry from an executable, even if the plt refcount goes to 0.