In some situations, futex() is called even when lzma
support is not compiled in. Let's enable it unconditionally
for now.

https://bugs.gentoo.org/771096
https://bugs.astron.com/view.php?id=241
--- a/src/seccomp.c
+++ b/src/seccomp.c
@@ -175,9 +175,7 @@ enable_sandbox_full(void)
  	ALLOW_RULE(fcntl64);
 	ALLOW_RULE(fstat);
  	ALLOW_RULE(fstat64);
-#ifdef XZLIBSUPPORT
 	ALLOW_RULE(futex);
-#endif
 	ALLOW_RULE(getdents);
 #ifdef __NR_getdents64
 	ALLOW_RULE(getdents64);