base: destruct signal receiver platform specific

This is made for future signal framework in base-hw
wich needs a platform specific hook in the signal-
receiver destruction.

ref #589

base-hw/src/base/signal/signal.cc

@@ -199,3 +199,5 @@ Signal Signal_receiver::wait_for_signal()
 void Signal_receiver::local_submit(Signal::Data signal) {
 	PDBG("Not implemented"); };
 
+
+void Signal_receiver::_platform_destructor() { }

base/include/base/signal.h

@@ -251,6 +251,11 @@ namespace Genode {
 			 */
 			void _unsynchronized_dissolve(Signal_context *context);
 
+			/**
+			 * Hook to platform specific destructor parts
+			 */
+			void _platform_destructor();
+
 		public:
 
 			/**

base/src/base/signal/common.cc

@@ -69,5 +69,6 @@ Signal_receiver::~Signal_receiver()
 	/* disassociate contexts from the receiver */
 	for (List_element<Signal_context> *le; (le = _contexts.first()); )
 		_unsynchronized_dissolve(le->object());
-}
 
+	_platform_destructor();
+}

base/src/base/signal/signal.cc

@@ -400,3 +400,6 @@ void Signal_receiver::dispatch_signals(Signal_source *signal_source)
 		context->_lock.unlock();
 	}
 }
+
+
+void Signal_receiver::_platform_destructor() { }