PowerPC64 --emit-relocs support for notoc stubs

PowerPC64 --emit-relocs support for notoc stubs

This patch uses the newly defined high-part REL16 relocs to emit
relocations on the notoc stubs as we already do for other stubs.

	* elf64-ppc.c (num_relocs_for_offset): New function.
	(emit_relocs_for_offset): New function.
	(use_global_in_relocs): New function, split out from..
	(ppc_build_one_stub): ..here.  Output relocations for notoc stubs.
	(ppc_size_one_stub): Calculate reloc count for notoc stubs.
	(ppc64_elf_size_stubs): Don't count undefined syms in stub_globals.