PowerPC64 DT_RELR relative reloc addresses

Section addresses can change between ppc64_elf_size_stubs and
ppc64_elf_build_stubs due to .eh_frame editing.  The idea of stashing
r_offset final addresses calculated in ppc64_elf_size_stubs for use by
ppc64_elf_build_stubs was never a good idea.  Instead, we need to keep
section/offset pairs.

	* elf64-ppc.c (struct ppc_link_hash_table): Delete relr_addr.
	Add relr section/offset array.
	(append_relr_off): Rewrite.  Update all callers.
	(sort_relr): New function.
	(ppc64_elf_size_stubs): Adjust to suit new relative reloc stash.
	(ppc64_elf_build_stubs): Likewise.

(cherry picked from commit 0aac2413)
(cherry picked from commit e26ff4b5)