seccomp: update for Ubuntu 18.04

Add new syscalls (getrandom).

The resolver now uses openat(2) and sendmsg(2).

src/xmppipe_sandbox_seccomp.c

@@ -107,6 +107,9 @@ xmppipe_sandbox_init(xmppipe_state_t *state)
 #ifdef __NR_send
         SC_ALLOW(send),
 #endif
+#ifdef __NR_sendmsg
+        SC_ALLOW(sendmsg),
+#endif
 #ifdef __NR_sendmmsg
         SC_ALLOW(sendmmsg),
 #endif
@@ -130,6 +133,9 @@ xmppipe_sandbox_init(xmppipe_state_t *state)
 #ifdef __NR_open
         SC_ALLOW(open),
 #endif
+#ifdef __NR_openat
+        SC_ALLOW(openat),
+#endif
 #ifdef __NR_close
         SC_ALLOW(close),
 #endif
@@ -183,6 +189,9 @@ xmppipe_sandbox_init(xmppipe_state_t *state)
 #ifdef __NR_fstat64
         SC_ALLOW(fstat64),
 #endif
+#ifdef __NR_getrandom
+        SC_ALLOW(getrandom),
+#endif
 
 #ifdef __NR_getppid
         SC_ALLOW(getppid),