ELFv2 stub, plt and glink changes

ELFv2 stub, plt and glink changes

An ELFv2 PLT entry is simply the address of the target function rather
than three (or two) words to specify entry, toc and static chain.  PLT
call stubs are correspondingly simpler and need no thread safety
barrier.  The glink resolver stub and branch table also is simplified,
a change that could be applied to ELFv1 too, but isn't as yet.

	* elf64-ppc.c (PLT_ENTRY_SIZE, PLT_INITIAL_ENTRY_SIZE): Add htab
	parameter and adjust for ELFv2.  Update all uses.
	(PLT_CALL_STUB_SIZE): Delete.
	(ppc64_elf_get_synthetic_symtab): Support new glink layout.
	(allocate_dynrelocs): Likewise.
	(plt_stub_size, build_plt_stub): Adjust for ELFv2.
	(get_r2off): Return 0 for ELFv2 -R.
	(ppc_build_one_stub, ppc_size_one_stub): Adjust for ELFv2.
	(ppc64_elf_size_stubs): Likewise.
	(ppc64_elf_build_stubs): Add new ELFv2 glink.