Added test for proper scheduling after delay expiry

It's not obvious from the FreeRTOS source code (in tasks.c) what
happens if a task's delay ends while another task of the same priority
is running.
This test demonstrates that the running task continues.

  * test-stm32f4/action_after_delay-main.adb,
    test-stm32f4/action_after_delay.adb,
    test-stm32f4/action_after_delay.ads: new test.
  * test-stm32f4/testbed.gpr: include action_after_delay.

test-stm32f4/action_after_delay-main.adb

@@ -0,0 +1,14 @@
+--  Copyright (C) 2020 Free Software Foundation, Inc.
+
+--  This file is part of the Cortex GNAT RTS package.
+--
+--  Copying and distribution of this file, with or without
+--  modification, are permitted in any medium without royalty provided
+--  the copyright notice and this notice are preserved.  This file is
+--  offered as-is, without any warranty.
+
+with Ada.Real_Time;
+procedure Action_After_Delay.Main is
+begin
+   delay until Ada.Real_Time.Time_Last;
+end Action_After_Delay.Main;

test-stm32f4/action_after_delay.adb

@@ -0,0 +1,38 @@
+--  Copyright (C) 2020 Free Software Foundation, Inc.
+
+--  This file is part of the Cortex GNAT RTS package.
+--
+--  Copying and distribution of this file, with or without
+--  modification, are permitted in any medium without royalty provided
+--  the copyright notice and this notice are preserved.  This file is
+--  offered as-is, without any warranty.
+
+with Ada.Real_Time;
+
+package body Action_After_Delay is
+
+   task T1;
+   task T2;
+
+   T2_Has_Run : Boolean := False with Volatile;
+
+   task body T1 is
+   begin
+      loop
+         exit when T2_Has_Run;
+      end loop;
+      --  PE here (because it's illegal in Ravenscar to exit a task)
+      --  if T2 has run
+   end T1;
+
+   task body T2 is
+      use type Ada.Real_Time.Time;
+   begin
+      delay until Ada.Real_Time.Clock + Ada.Real_Time.Seconds (1);
+      --  Shouldn't get here, since T1 hasn't reached a dispatching
+      --  point.
+      T2_Has_Run := True;
+      delay until Ada.Real_Time.Time_Last;
+   end T2;
+
+end Action_After_Delay;

test-stm32f4/action_after_delay.ads

@@ -0,0 +1,15 @@
+--  Copyright (C) 2020 Free Software Foundation, Inc.
+
+--  This file is part of the Cortex GNAT RTS package.
+--
+--  Copying and distribution of this file, with or without
+--  modification, are permitted in any medium without royalty provided
+--  the copyright notice and this notice are preserved.  This file is
+--  offered as-is, without any warranty.
+
+--  The purpose of this little suite is to determine what happens when
+--  one task is running and another, at the same priority, exits a
+--  delay; will it run or be blocked?
+
+package Action_After_Delay with Elaborate_Body is
+end Action_After_Delay;

test-stm32f4/testbed.gpr

@@ -19,6 +19,7 @@
 project Testbed is
 
    for Main use ("testbed.adb",
+                 "action_after_delay-main.adb",
                  "delay_in_po-main.adb",
                  "generate_hard_fault.adb");
    for Languages use ("Ada", "C");
@@ -29,6 +30,7 @@ project Testbed is
    for Runtime ("ada") use project'Project_Dir & "../local/stm32f4";
 
    package Builder is
+      for Executable ("action_after_delay-main.adb") use "action_after_delay";
       for Executable ("delay_in_po-main.adb") use "delay_in_po";
       for Global_Configuration_Pragmas use "gnat.adc";
       for Global_Compilation_Switches ("ada") use