Revert PR16467 change

Revert PR16467 change

This reverts the pr16467 change, which was incorrect due to faulty
analysis of the pr16467 testcase.  The failure was not due to a
mismatch in symbol type (ifunc/non-ifunc) but due to a symbol loop
being set up.

See https://sourceware.org/ml/binutils/2016-06/msg00013.html for some
rambling on versioned symbols and ELF shared library symbol overriding
that explain this patch.

bfd/
	PR ld/20159
	PR ld/16467
	* elflink.c (_bfd_elf_merge_symbol): Revert PR16467 change.
	(_bfd_elf_add_default_symbol): Don't indirect to/from defined
	symbol given a version by a script different to the version
	of the symbol being added.
	(elf_link_add_object_symbols): Use _bfd_elf_strtab_save and
	_bfd_elf_strtab_restore.  Don't fudge dynstr references.
	* elf-strtab.c (_bfd_elf_strtab_restore_size): Delete.
	(struct strtab_save): New.
	(_bfd_elf_strtab_save, _bfd_elf_strtab_restore): New functions.
	* elf-bfd.h (_bfd_elf_strtab_restore_size): Delete.
	(_bfd_elf_strtab_save, _bfd_elf_strtab_restore): Declare.