get_synthetic_symtab fixes for commit 68bbe1183379

get_synthetic_symtab fixes for commit 68bbe1183379

Given that relocation symbol name can now be NULL for ELF, adjust
various get_synthetic_symtab routines so they don't segfault.

	* elf.c (_bfd_elf_get_synthetic_symtab): Cope with sym->name
	possibly being NULL.
	* elf32-arm.c (elf32_arm_get_synthetic_symtab): Likewise.
	* elf32-ppc.c (ppc_elf_get_synthetic_symtab): Likewise.
	* elf64-ppc.c (ppc64_elf_get_synthetic_symtab): Likewise.
	* elfxx-mips.c (_bfd_mips_elf_get_synthetic_symtab): Likewise.
	* elfxx-x86.c (_bfd_x86_elf_get_synthetic_symtab): Likewise.