Fix previous change to use defined()

src/lxc/utils.h

@@ -56,7 +56,7 @@ static inline int setns(int fd, int nstype)
 {
 #ifdef __NR_setns
 	return syscall(__NR_setns, fd, nstype);
-#elif __NR_set_ns
+#elif defined(__NR_set_ns)
 	return syscall(__NR_set_ns, fd, nstype);
 #else
 	errno = ENOSYS;