PowerPC64 TLS optimization fix

When linking with --no-tls-optimize the linker doesn't generate a call
or long branch stub to __tls_get_addr in some circumstances, giving:

relocation truncated to fit: R_PPC64_REL24 against symbol `__tls_get_addr'

	* elf64-ppc.c (ppc64_elf_size_stubs): Correct condition under
	which __tls_get_addr calls will be eliminated.

(cherry picked from commit abc489c6)