There are occasions where someone might want to build a 64-bit
pc-relative offset from 16-bit pieces.  This adds the necessary REL16
relocs corresponding to existing ADDR16 relocs that can be used to
build 64-bit absolute values.

include/
	* elf/ppc64.h (R_PPC64_REL16_HIGH, R_PPC64_REL16_HIGHA),
	(R_PPC64_REL16_HIGHER, R_PPC64_REL16_HIGHERA),
	(R_PPC64_REL16_HIGHEST, R_PPC64_REL16_HIGHESTA): Define.
	(R_PPC64_LO_DS_OPT, R_PPC64_16DX_HA): Bump value.
bfd/
	* reloc.c (BFD_RELOC_PPC64_REL16_HIGH, BFD_RELOC_PPC64_REL16_HIGHA),
	(BFD_RELOC_PPC64_REL16_HIGHER, BFD_RELOC_PPC64_REL16_HIGHERA),
	(BFD_RELOC_PPC64_REL16_HIGHEST, BFD_RELOC_PPC64_REL16_HIGHESTA):
	Define.
	* elf64-ppc.c (ppc64_elf_howto_raw): Add new REL16 howtos.
	(ppc64_elf_reloc_type_lookup): Translate new REL16 relocs.
	(ppc64_elf_check_relocs, ppc64_elf_relocate_section): Handle them.
	* bfd-in2.h: Regenerate.
	* libbfd.h: Regenerate.
gas/
	* config/tc-ppc.h (TC_FORCE_RELOCATION_SUB_LOCAL): Allow ADDR16
	HIGH, HIGHA, HIGHER, HIGHERA, HIGHEST, and HIGHESTA relocs.
	Group 16-bit relocs.
	* config/tc-ppc.c (md_apply_fix): Translate those ADDR16 relocs
	to REL16 when pcrel.  Sort relocs.