gcc compilation fix.

src/ChunkDef.h

@@ -399,9 +399,12 @@ public:
 typedef std::list<cChunkCoords> cChunkCoordsList;
 typedef std::vector<cChunkCoords> cChunkCoordsVector;
 
+namespace std
+{
+
 /** A simple hash function for chunk coords, we assume that chunk coords won't use more than 16 bits, so the hash is almost an identity.
 Used for std::unordered_map<cChunkCoords, ...> */
-template<> struct std::hash<cChunkCoords>
+template<> struct hash<cChunkCoords>
 {
 	size_t operator ()(const cChunkCoords & a_Coords)
 	{
@@ -409,6 +412,8 @@ template<> struct std::hash<cChunkCoords>
 	}
 };
 
+}  // namespace std
+