Move std::string str_validate to separate header

This is to fix compilation of squirrel on MacOS/clang, as squirrel
defines macros which clash with including <string>

source.list

@@ -344,6 +344,7 @@ story_type.h
 strgen/strgen.h
 string_base.h
 string_func.h
+string_func_extra.h
 string_type.h
 stringfilter_type.h
 strings_func.h

src/saveload/saveload.cpp

@@ -41,6 +41,7 @@
 #include "../fileio_func.h"
 #include "../gamelog.h"
 #include "../string_func.h"
+#include "../string_func_extra.h"
 #include "../fios.h"
 #include "../error.h"
 

src/string_func.h

@@ -27,7 +27,6 @@
 #define STRING_FUNC_H
 
 #include <stdarg.h>
-#include <string>
 
 #include "core/bitmath_func.hpp"
 #include "string_type.h"
@@ -56,13 +55,6 @@ static inline void str_validate(char *str, const char *last, StringValidationSet
 	*str_validate_intl(str, last, settings) = '\0';
 }
 
-static inline void str_validate(std::string &str, StringValidationSettings settings = SVS_REPLACE_WITH_QUESTION_MARK)
-{
-	if (str.empty()) return;
-	char *buf = const_cast<char *>(str.c_str());
-	str.resize(str_validate_intl(buf, buf + str.size(), settings) - buf);
-}
-
 void ValidateString(const char *str);
 
 void str_fix_scc_encoded(char *str, const char *last);

src/string_func_extra.h

@@ -0,0 +1,23 @@
+/* $Id$ */
+
+/*
+ * 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/>.
+ */
+
+#ifndef STRING_FUNC_EXTRA_H
+#define STRING_FUNC_EXTRA_H
+
+#include "string_func.h"
+#include <string>
+
+static inline void str_validate(std::string &str, StringValidationSettings settings = SVS_REPLACE_WITH_QUESTION_MARK)
+{
+	if (str.empty()) return;
+	char *buf = const_cast<char *>(str.c_str());
+	str.resize(str_validate_intl(buf, buf + str.size(), settings) - buf);
+}
+
+#endif /* STRING_FUNC_EXTRA_H */