Add system-level at_exit handlers for safe resource cleanup

src/crystal/at_exit_handlers.cr

@@ -1,11 +1,16 @@
 # :nodoc:
 module Crystal::AtExitHandlers
   private class_getter(handlers) { [] of Int32, ::Exception? -> }
+  private class_getter(internal_handlers) { [] of Int32, ::Exception? -> }
 
   def self.add(handler)
     handlers << handler
   end
 
+  def self.__crystal_add(handler)
+    internal_handlers << handler
+  end
+
   def self.run(status, exception = nil)
     if handlers = @@handlers
       # Run the registered handlers in reverse order
@@ -19,6 +24,18 @@ module Crystal::AtExitHandlers
       end
     end
 
+    if internal_handlers = @@internal_handlers
+      # Run the registered internal handlers in reverse order
+      while handler = internal_handlers.pop?
+        begin
+          handler.call status, exception
+        rescue handler_ex
+          Crystal::System.print_error "Error running internal at_exit handler: %s\n", handler_ex.message || ""
+          status = 1 if status.zero?
+        end
+      end
+    end
+
     status
   end
 end