base: restructure signal-submit initialization

This patch allows core's 'Signal_transmitter' implementation to sidestep
the 'Env::Pd' interface and thereby adhere to a stricter layering within
core. The 'Signal_transmitter' now uses - on kernels that depend on it -
a dedicated (and fairly freestanding) RPC proxy mechanism for signal
deliver, instead of channeling signals through the 'Pd_session::submit'
RPC function.

repos/base-nova/src/lib/base/signal_transmitter.cc

@@ -11,18 +11,23 @@
  * under the terms of the GNU Affero General Public License version 3.
  */
 
-
 /* Genode includes */
 #include <base/signal.h>
 #include <base/log.h>
 #include <base/trace/events.h>
 
+/* base-internal includes */
+#include <base/internal/globals.h>
+
 /* NOVA includes */
 #include <nova/syscalls.h>
 
 using namespace Genode;
 
 
+void Genode::init_signal_transmitter(Env &) { }
+
+
 void Signal_transmitter::submit(unsigned cnt)
 {
 	{