score: Add _Thread_Dispatch_direct_no_return()

The __builtin_unreachable() cannot be used with current GCC versions to
tell the compiler that a function does not return to the caller, see:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99151

Add a no return variant of _Thread_Dispatch_direct() to avoid generation
of dead code.

cpukit/include/rtems/score/threaddispatch.h

@@ -125,6 +125,17 @@ void _Thread_Dispatch( void );
  */
 void _Thread_Dispatch_direct( Per_CPU_Control *cpu_self );
 
+/**
+ * @brief Directly do a thread dispatch and do not return.
+ *
+ * @param cpu_self is the current processor.
+ *
+ * @see _Thread_Dispatch_direct().
+ */
+RTEMS_NO_RETURN void _Thread_Dispatch_direct_no_return(
+  Per_CPU_Control *cpu_self
+);
+
 /**
  * @brief Performs a thread dispatch on the current processor.
  *

cpukit/posix/src/pthreadexit.c

@@ -35,6 +35,6 @@ void pthread_exit( void *value_ptr )
 
   _Thread_Exit( executing, THREAD_LIFE_TERMINATING, value_ptr );
 
-  _Thread_Dispatch_direct( cpu_self );
+  _Thread_Dispatch_direct_no_return( cpu_self );
   RTEMS_UNREACHABLE();
 }

cpukit/rtems/src/taskexit.c

@@ -42,6 +42,6 @@ void rtems_task_exit( void )
     NULL
   );
 
-  _Thread_Dispatch_direct( cpu_self );
+  _Thread_Dispatch_direct_no_return( cpu_self );
   RTEMS_UNREACHABLE();
 }

cpukit/score/src/threaddispatch.c

@@ -358,6 +358,9 @@ void _Thread_Dispatch_direct( Per_CPU_Control *cpu_self )
   _Thread_Do_dispatch( cpu_self, level );
 }
 
+RTEMS_ALIAS( _Thread_Dispatch_direct ) void
+_Thread_Dispatch_direct_no_return( Per_CPU_Control * );
+
 void _Thread_Dispatch_enable( Per_CPU_Control *cpu_self )
 {
   uint32_t disable_level = cpu_self->thread_dispatch_disable_level;

cpukit/score/src/threadrestart.c

@@ -288,7 +288,7 @@ void _Thread_Life_action_handler(
   if ( _Thread_Is_life_terminating( previous_life_state ) ) {
     cpu_self = _Thread_Wait_for_join( executing, cpu_self );
     _Thread_Make_zombie( executing );
-    _Thread_Dispatch_direct( cpu_self );
+    _Thread_Dispatch_direct_no_return( cpu_self );
     RTEMS_UNREACHABLE();
   }
 
@@ -610,7 +610,7 @@ void _Thread_Restart_self(
   _Thread_Wait_release_default( executing, lock_context );
 
   _Thread_Priority_update( &queue_context );
-  _Thread_Dispatch_direct( cpu_self );
+  _Thread_Dispatch_direct_no_return( cpu_self );
   RTEMS_UNREACHABLE();
 }