Allow (but return EACCES) fstatat64 in sandbox.

This is apparently used in some configurations of OpenSSL when glibc
has getrandom().  bz#3276, patch from Kris Karas, ok djm@
diff --git a/sandbox-seccomp-filter.c b/sandbox-seccomp-filter.c
index d8dc712..7981c84 100644
--- a/sandbox-seccomp-filter.c
+++ b/sandbox-seccomp-filter.c
@@ -154,6 +154,9 @@
 #ifdef __NR_fstat64
 	SC_DENY(__NR_fstat64, EACCES),
 #endif
+#ifdef __NR_fstatat64
+	SC_DENY(__NR_fstatat64, EACCES),
+#endif
 #ifdef __NR_open
 	SC_DENY(__NR_open, EACCES),
 #endif