Return reloc_class_ifunc for reloc against IFUNC

Return reloc_class_ifunc for reloc against IFUNC

elf_XXX_reloc_type_class should return reloc_class_ifunc for relocation
against STT_GNU_IFUNC symbol.

bfd/

	PR ld/18841
	* elf-bfd.h (elf_link_hash_table): Add dynsym.
	* elf32-i386.c (elf_i386_reloc_type_class): Return
	reloc_class_ifunc for relocation against STT_GNU_IFUNC symbol.
	* elf64-x86-64.c (elf_x86_64_reloc_type_class): Likewise.
	* elflink.c (_bfd_elf_link_create_dynamic_sections): Set dynsym.
	(bfd_elf_size_dynsym_hash_dynstr): Use dynsym.
	(elf_final_link_info): Remove dynsym_sec.
	(elf_link_output_extsym): Replace dynsym_sec with dynsym.
	(bfd_elf_final_link): Remove reference to dynsym_sec.  Replace
	dynsym_sec with dynsym.

ld/testsuite/

	PR ld/18841
	* ld-ifunc/ifunc.exp: Add a test for PR ld/18841.
	* ld-ifunc/pr18841.out: New file.
	* ld-ifunc/pr18841a.c: Likewise.
	* ld-ifunc/pr18841b.c: Likewise.