s390x: Enable nptl for s390x

S390x user emulation can do nptl. Reflect this in the configure script.
Signed-off-by: NUlrich Hecht <uli@suse.de>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

configure

@@ -3150,6 +3150,7 @@ case "$target_arch2" in
     target_phys_bits=64
   ;;
   s390x)
+    target_nptl="yes"
     target_phys_bits=64
   ;;
   *)