PR29540, R_PPC64_NONE in .rela.dyn when linking Linux vdso

	PR 29540
	* elf64-ppc.c (allocate_dynrelocs): Don't alloc space for relocs
	against discarded sections.
	(ppc64_elf_size_dynamic_sections): Use standard test for discarded
	sections.
	* elf32-ppc.c (allocate_dynrelocs): Don't alloc space for relocs
	against discarded sections.
	(ppc_elf_size_dynamic_sections): Use standard test for discarded
	sections.