PowerPC64 dot-symbol compatibility bugfixes

PowerPC64 dot-symbol compatibility bugfixes

Lots of fixes for the compatibility code that handles linking of
-mcall-aixdesc code (or that generated by 12 year old gcc) with
current ELFv1 ABI code.

1) A reference to a dot-symbol in an object file wasn't satisfied by a
   function descriptor in later object files.
2) The as-needed code had bit-rotted;  Shared libs now need a strong
   reference to be counted as needed.
3) --gc-sections involving dot-symbols was broken, needing
   func_desc_adjust to be run early and lots of other fixes.

bfd/
	* elf64-ppc.c (struct ppc_link_hash_entry): Delete "was_undefined".
	(struct ppc_link_hash_table): Delete "twiddled_syms".  Add
	"need_func_desc_adj".
	(lookup_fdh): Link direct fdh sym via oh field and set flags.
	(make_fdh): Make strong and weak undefined function descriptor
	symbols.
	(ppc64_elf_merge_symbol): New function.
	(elf_backend_merge_symbol): Define.
	(ppc64_elf_archive_symbol_lookup): Don't test undefweak for fake
	function descriptors.
	(add_symbol_adjust): Don't twiddle symbols to undefweak.
	Propagate more ref flags to function descriptor symbol.  Make
	some function descriptor symbols dynamic.
	(ppc64_elf_before_check_relocs): Only run add_symbol_adjust for
	ELFv1.  Set need_func_desc_adj.  Don't fix undefs list.
	(ppc64_elf_check_relocs): Set non_ir_ref for descriptors.
	Don't call lookup_fdh here.
	(ppc64_elf_gc_sections): New function.
	(bfd_elf64_bfd_gc_sections): Define.
	(ppc64_elf_gc_mark_hook): Mark descriptor.
	(func_desc_adjust): Don't make fake function descriptor syms strong
	here.  Exit earlier on non-dotsyms.  Take note of elf.dynamic
	flag when deciding whether a dynamic function descriptor might
	be needed.  Transfer elf.dynamic and set elf.needs_plt.  Move
	plt regardless of visibility.  Make descriptor dynamic if
	entry sym is dynamic, not for other cases.
	(ppc64_elf_func_desc_adjust): Don't run func_desc_adjust if
	already done.
	(ppc64_elf_edit_opd): Use oh field rather than lookup_fdh.
	(ppc64_elf_size_stubs): Likewise.
	(ppc_build_one_stub): Don't clear was_undefined.  Only set sym
	undefweak if stub symbol is defined.
	(undo_symbol_twiddle, ppc64_elf_restore_symbols): Delete.
	* elf64-ppc.h (ppc64_elf_restore_symbols): Don't declare.
ld/
	* emultempl/ppc64elf.em (gld${EMULATION_NAME}_finish): Don't call
	ppc64_elf_restore_symbols.
	* testsuite/ld-powerpc/dotsym1.d: New.
	* testsuite/ld-powerpc/dotsym2.d: New.
	* testsuite/ld-powerpc/dotsym3.d: New.
	* testsuite/ld-powerpc/dotsym4.d: New.
	* testsuite/ld-powerpc/dotsymref.s: New.
	* testsuite/ld-powerpc/nodotsym.s: New.
	* testsuite/ld-powerpc/powerpc.exp: Run new tests.