[GOLD] PowerPC relocations for prefix insns

[GOLD] PowerPC relocations for prefix insns

Also use pc-relative instructions for notoc stubs.

elfcpp/
	* powerpc.h (R_PPC64_PCREL_OPT, R_PPC64_D34, R_PPC64_D34_LO),
	(R_PPC64_D34_HI30, R_PPC64_D34_HA30, R_PPC64_PCREL34),
	(R_PPC64_GOT_PCREL34, R_PPC64_PLT_PCREL34, R_PPC64_PLT_PCREL34_NOTOC),
	(R_PPC64_ADDR16_HIGHER34, R_PPC64_ADDR16_HIGHERA34),
	(R_PPC64_ADDR16_HIGHEST34, R_PPC64_ADDR16_HIGHESTA34),
	(R_PPC64_REL16_HIGHER34, R_PPC64_REL16_HIGHERA34),
	(R_PPC64_REL16_HIGHEST34, R_PPC64_REL16_HIGHESTA34),
	(R_PPC64_D28, R_PPC64_PCREL28): Define.
gold/
	* powerpc.cc (Target_powerpc): Add powerxx_stubs_ and accessor
	functions.
	(Target_powerpc::maybe_skip_tls_get_addr_call): Handle PLT_PCREL34
	and PLT_PCREL34_NOTOC relocs.
	(Powerpc_relocate_functions): Add addr34, addr34_hi, addr34_ha,
	addr28, addr16_higher34, addr16_highera34, addr16_highest34,
	addr16_highest34a functions.
	(li_11_0, ori_11_11_0, sldi_11_11_34): Define.
	(paddi_12_pc, pld_12_pc, pnop): Define.
	(d34, ha34): New inline functions.
	(Stub_table::add_plt_call_entry): Handle powerxx_stubs.
	(Stub_table::add_eh_frame): Likewise.
	(build_powerxx_offset): New function.
	(Stub_table::plt_call_size): Handle powerxx_stubs.
	(Stub_table::branch_stub_size): Likewise.
	(Stub_table::do_write): Likewise.
	(Target_powerpc::Scan::get_reference_flags): Handle new relocs.
	(Target_powerpc::Scan::reloc_needs_plt_for_ifunc: Likewise.
	(Target_powerpc::Scan::local, global, relocate): Likewise.