Posix: Fix no task switching issue if a task ended its main function (#184)

* Posix: Fix no task switching issue if a task ended

When the main function of a task exits, no task switching happened.
This is because all the remaining tasks are waiting on the condition
variable. The fix is to trigger a task switch and mark the exiting
task as "Dying" to be suspened and exited properly from the scheduler.

* Posix: Assert and stop if the Task function returned

* Posix: just assert if a task returned from its main function

Co-authored-by: alfred gedeon <alfred2g@hotmail.com>

portable/ThirdParty/GCC/Posix/port.c

@@ -430,6 +430,13 @@ Thread_t *pxThread = pvParams;
 	/* Call the task's entry point. */
 	pxThread->pxCode( pxThread->pvParams );
 
+	/* A function that implements a task must not exit or attempt to return to
+	* its caller as there is nothing to return to. If a task wants to exit it
+	* should instead call vTaskDelete( NULL ). Artificially force an assert()
+	* to be triggered if configASSERT() is defined, so application writers can
+        * catch the error. */
+	configASSERT( pdFALSE );
+
 	return NULL;
 }
 /*-----------------------------------------------------------*/