x64: Fix R_X86_64_TPOFF64 relocation without symbol

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Sergei Turukin <sergei.turukin@rackspace.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>