Codechange: replace error/usererror printf variant with fmt variant and rename

src/error_func.h

@@ -0,0 +1,20 @@
+/*
+ * 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 error_func.h Error reporting related functions. */
+
+#ifndef ERROR_FUNC_H
+#define ERROR_FUNC_H
+
+#include "3rdparty/fmt/format.h"
+
+void NORETURN UserErrorI(const std::string &str);
+void NORETURN FatalErrorI(const std::string &str);
+#define UserError(format_string, ...) UserErrorI(fmt::format(FMT_STRING(format_string), ## __VA_ARGS__))
+#define FatalError(format_string, ...) FatalErrorI(fmt::format(FMT_STRING(format_string), ## __VA_ARGS__))
+
+#endif /* ERROR_FUNC_H */