PowerPC GOT_PCREL34 optimisation

PowerPC GOT_PCREL34 optimisation

bfd/
	* elf64-ppc.c (ppc64_elf_check_relocs): Set has_gotrel for
	R_PPC64_GOT_PCREL34.
	(xlate_pcrel_opt): New function.
	(ppc64_elf_edit_toc): Handle R_PPC64_GOT_PCREL34.
	(ppc64_elf_relocate_section): Edit GOT indirect to GOT relative
	for R_PPC64_GOT_PCREL34.  Implement R_PPC64_PCREL_OPT optimisation.
ld/
	* testsuite/ld-powerpc/pcrelopt.s,
	* testsuite/ld-powerpc/pcrelopt.d,
	* testsuite/ld-powerpc/pcrelopt.sec: New test.
	* testsuite/ld-powerpc/powerpc.exp: Run it.