HAL: Use extern "C" in implementation files.

This turns accidental parameter mismatches between header and implementation
into compiler errors.

Change-Id: Ic26fabb82b2fd5f79407a11435cdbd35348af15f

hal/lib/Athena/Notifier.cpp

@@ -59,6 +59,8 @@ static void cleanupNotifierAtExit() {
 	notifierManager = nullptr;
 }
 
+extern "C" {
+
 void* initializeNotifier(void (*process)(uint64_t, void*), void *param, int32_t *status)
 {
 	if (!process) {
@@ -154,3 +156,5 @@ void stopNotifierAlarm(void* notifier_pointer, int32_t *status)
 	Notifier* notifier = (Notifier*)notifier_pointer;
 	notifier->triggerTime = UINT64_MAX;
 }
+
+}  // extern "C"