Permit usage of std::unordered_map & std::unorderered_set on c++11 compilers (#4430)

This fallback to std::map & std::set for older compilers

Use UNORDERED_SET as an example in decoration and ore biome sets

Use UNORDERED_MAP as an example in nameidmapping

src/util/cpp11_container.h

@@ -0,0 +1,35 @@
+/*
+Minetest
+Copyright (C) 2016 nerzhul, Loic Blot <loic.blot@unix-experience.fr>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program 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 Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#ifndef MT_CPP11CONTAINER_HEADER
+#define MT_CPP11CONTAINER_HEADER
+
+#if __cplusplus >= 201103L
+	#include <unordered_map>
+	#include <unordered_set>
+	#define UNORDERED_MAP std::unordered_map
+	#define UNORDERED_SET std::unordered_set
+#else
+	#include <map>
+	#include <set>
+	#define UNORDERED_MAP std::map
+	#define UNORDERED_SET std::set
+#endif
+
+#endif