Core/Posix: Add absolutly not tested File::SetSize implementation

At least the engine should compile again on posix


Former-commit-id: c2ccdb9ad939b20e288b211aee678917934f1757

src/Nazara/Core/Posix/FileImpl.hpp

@@ -39,6 +39,7 @@ namespace Nz
 			bool Open(const String& filePath, UInt32 mode);
 			std::size_t Read(void* buffer, std::size_t size);
 			bool SetCursorPos(CursorPosition pos, Int64 offset);
+			bool SetSize(UInt64 size);
 			std::size_t Write(const void* buffer, std::size_t size);
 
 			FileImpl& operator=(const FileImpl&) = delete;