Fix some compilation warnings.

Redone the commit based on the input in
https://github.com/godotengine/godot/pull/7851 . Not all warnings were
fixed but it's a start.

platform/x11/os_x11.cpp

@@ -1241,7 +1241,7 @@ static Property read_property(Display* p_display, Window p_window, Atom p_proper
 
 	}while(bytes_after != 0);
 
-	Property p = {ret, actual_format, nitems, actual_type};
+	Property p = {ret, actual_format, (int)nitems, actual_type};
 
 	return p;
 }