Add .abiversion related support for ELFv2

Add .abiversion related support for ELFv2

Defines bits in ELF e_flags to differentiate ELFv2 objects from ELFv2,
adds .abiversion directive to explicitly choose the ABI, and code to
check and automatically select ABI.

include/elf/
	* ppc64.h (EF_PPC64_ABI): Define.
bfd/
	* elf64-ppc.c (abiversion, set_abiversion): New functions.
	(ppc64_elf_get_synthetic_symtab): Handle ELFv2 objects without .opd.
	(struct ppc_link_hash_table): Add opd_abi.
	(ppc64_elf_check_relocs): Check no .opd with ELFv2.
	(ppc64_elf_merge_private_bfd_data): New function.
	(ppc64_elf_print_private_bfd_data): New function.
	(ppc64_elf_tls_setup): Set htab->opd_abi.
	(ppc64_elf_size_dynamic_sections): Don't emit OPD related dynamic
	tags for ELFv2.
	(ppc_build_one_stub): Use R_PPC64_IRELATIVE for ELFv2 ifunc.
	(ppc64_elf_finish_dynamic_symbol): Likewise
binutils/
	* readelf.c (get_machine_flags): Display ABI version for EM_PPC64.
gas/
	* config/tc-ppc.c: Include elf/ppc64.h.
	(ppc_abiversion): New variable.
	(md_pseudo_table): Add .abiversion.
	(ppc_elf_abiversion, ppc_elf_end): New functions.
	* config/tc-ppc.h (md_end): Define.