Codechange: Let the compile generate the master command table out of templated command traits.

This is using a non-intrusive type-traits like templated system, which
allows compile-time validation that the command table and the command
enum match up.

src/viewport_cmd.h

@@ -0,0 +1,19 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file viewport_cmd.h Command definitions related to viewports. */
+
+#ifndef VIEWPORT_CMD_H
+#define VIEWPORT_CMD_H
+
+#include "command_type.h"
+
+CommandProc CmdScrollViewport;
+
+DEF_CMD_TRAIT(CMD_SCROLL_VIEWPORT, CmdScrollViewport, CMD_DEITY, CMDT_OTHER_MANAGEMENT)
+
+#endif /* VIEWPORT_CMD_H */