Sparc v9 ABI compliant PLT:

* elf64-sparc.c (PLT_HEADER_SIZE): V9 ABI uses 4 entries.
(plt_templates, sparc64_elf_build_plt_entry): Delete.
(LARGE_PLT_THRESHOLD): New define.
(GOT_RESERVED_ENTRIES): V9 ABI only uses 1.
(sparc64_elf_build_plt): New function.
(sparc64_elf_plt_entry_offset): Likewise.
(sparc64_elf_plt_ptr_offset): Likewise.
(sparc64_elf_adjust_dynamic_symbol): Change h->plt_offset to
contain the index for convenience.  Skip the initial entries
in .rela.plt.
(sparc64_elf_size_dynamic_sections): Zero the allocated contents
memory for the benefit of .rela.plt.
(sparc64_elf_relocate_section): Call sparc64_elf_plt_entry_offset.
(sparc64_elf_finish_dynamic_symbol): Kill template stuff.  Use
sparc64_elf_plt_entry_offset & sparc64_elf_plt_ptr_offset for reloc.
(sparc64_elf_finish_dynamic_sections): DT_PLTGOT points to .plt.
Call sparc64_elf_build_plt.
(elf_backend_want_got_plt): No.
(elf_backend_plt_readonly): No.
(elf_backend_plt_alignment): 8.
* elf.c (_bfd_elf_close_and_cleanup): New function; free the shstrtab.
* elf-bfd.h (_bfd_elf_close_and_cleanup): Declare it.
* elfxx-target.h (bfd_elfNN_close_and_cleanup): Arrange for it
to be called.