PowerPC64, Don't copy weak symbol dyn_relocs to weakdef.

PowerPC64, Don't copy weak symbol dyn_relocs to weakdef.

At the cost of an extra field in the symbol table hash entries, this
simplification to the relocate_section dynamic reloc test should help
maintainability.

	* elf64-ppc.c (struct ppc_link_hash_entry): Add weakref.
	(ppc64_elf_copy_indirect_symbol): Set weakref.  Don't merge
	dyn_relocs for weakdefs.
	(alias_readonly_dynrelocs): New function.
	(ppc64_elf_adjust_dynamic_symbol): Use alias_readonly_dynrelocs.
	(ppc64_elf_relocate_section): Simplify condition under which
	dyn_relocs are emitted.