PowerPC ld segfault on script discarding dynamic sections

PowerPC ld segfault on script discarding dynamic sections

bfd/
	* elf64-ppc.c (ppc64_elf_finish_dynamic_sections): Don't segfault
	on .got or .plt output section being discarded by script.
	* elf32-ppc.c (ppc_elf_finish_dynamic_sections): Likewise.  Move
	vxworks splt temp.
gold/
	* powerpc.cc (Target_powerpc::make_iplt_section): Check that
	output_section exists before attempting add_output_section_data.
	(Target_powerpc::make_brlt_section): Likewise.