runtime: stub daemon symbol

Just so the symbol exists. We expect people to run their programs in foreground,
but if linked without lazy bindings, the symbol may be required.

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

runtime.cc

@@ -500,3 +500,9 @@ int prctl(int option, ...)
     errno = EINVAL;
     return -1;
 }
+
+int daemon(int nochdir, int noclose)
+{
+    WARN_STUBBED();
+    return -1;
+}