Fixes to powerpc64 gold ELFv2 support

Fixes to powerpc64 gold ELFv2 support

	* powerpc.cc (Target_powerpc::glink_section): Provide non-const
	accessor.
	(Target_powerpc::Branch_info::make_stub): Make global entry stubs.
	Only call ppc64_local_entry_offset for 64-bit.  Restrict
	symval_for_branch lookup to ELFv1.
	(Stub_table::add_plt_call_entry): Use unsigned int off.
	(Output_data_glink::Address, invalid_address): New.
	(Output_data_glink::add_eh_frame): Move out of line.  Add
	support for ELFv2.
	(Output_data_glink::add_global_entry, find_global_entry,
	global_entry_address): New functions.
	(Output_data_glink::global_entry_stubs_, end_branch_table_,
	ge_size): New variables.
	(Output_data_glink::set_final_data_size): Add global entry
	stub sizing.
	(Output_data_glink::do_write): Write global entry stubs.
	(Target_powerpc::Scan::reloc_needs_plt_for_ifunc): Add target
	parameter.  Return true for ELFv2.  Adjust callers.
	(Target_powerpc::Scan::local, global): Restrict opd lookup to
	ELFv1.  Similarly for ifunc and dynamic relocation processing
	specific to ELFv1.  Recognize that symbols are defined on
	their plt entries for ELFv2.
	(Target_powerpc::symval_for_branch): Assert if called for
	ELFv2 or ppc32.
	(Target_powerpc::Relocate::relocate): Use global entry plt
	stub for symbol value if such exists on ELFv2.
	(Target_powerpc::Relocate::relocate): Don't call
	symval_for_branch when ELFv2.  Do adjust for local entry
	offset when ELFv2.
	(Target_powerpc::do_dynsym_value): Set symbols to global entry
	plt stub for ELFv2.
	(Target_powerpc::do_plt_address_for_global): Similarly.