* configure.in (--enable-secureplt): New.

    * configure.in (--enable-secureplt): New.
        * elf64-alpha.c (INSN_LDA, INSN_LDAH, INSN_LDQ, INSN_BR): New.
        (INSN_SUBQ, INSN_S4SUBQ, INSN_JMP): New.
        (INSN_A, INSN_AB, INSN_ABC, INSN_ABO, INSN_AD): New.
        (elf64_alpha_use_secureplt): New.
        (OLD_PLT_HEADER_SIZE, OLD_PLT_ENTRY_SIZE): New.
        (NEW_PLT_HEADER_SIZE, NEW_PLT_ENTRY_SIZE): New.
        (PLT_HEADER_SIZE, PLT_ENTRY_SIZE): Conditionalize on secureplt.
        (ALPHA_ELF_LINK_HASH_PLT_LOC): Remove.
        (struct alpha_elf_link_hash_entry): Add plt_offset.
        (PLT_HEADER_WORD1, PLT_HEADER_WORD2, PLT_HEADER_WORD3): Remove.
        (PLT_HEADER_WORD4, PLT_ENTRY_WORD1, PLT_ENTRY_WORD2): Remove.
        (PLT_ENTRY_WORD3): Remove.
        (elf64_alpha_create_dynamic_sections): If secureplt, set SEC_READONLY
        on .plt and create .got.plt.
        (elf64_alpha_output_extsym): Remove .plt frobbing for symbol values.
        (get_got_entry): Initialize plt_offset.
        (elf64_alpha_want_plt): New.
        (elf64_alpha_check_relocs): Use it.
        (elf64_alpha_adjust_dynamic_symbol): Likewise.  Don't allocate
        plt entries here.
        (elf64_alpha_calc_got_offsets_for_symbol): Don't report internal
        error as user error.
        (elf64_alpha_size_plt_section_1): Allocate one plt entry per
        got subsection.
        (elf64_alpha_size_plt_section): Size .got.plt section.
        (elf64_alpha_size_rela_got_1): Don't allocate relocations if
        plt entries used.
        (elf64_alpha_size_dynamic_sections): Call elf64_alpha_size_plt_section.
        Add PLTRO DYNAMIC entry.
        (elf64_alpha_finish_dynamic_symbol): Generate secureplt format.
        (elf64_alpha_finish_dynamic_sections): Likewise.