[C++17] filesystem 크로스플랫폼 헤더

#ifndef INCLUDE_STD_FILESYSTEM_EXPERIMENTAL
#   if defined(__cpp_lib_filesystem)
#       define INCLUDE_STD_FILESYSTEM_EXPERIMENTAL 0
#   elif defined(__cpp_lib_experimental_filesystem)
#       define INCLUDE_STD_FILESYSTEM_EXPERIMENTAL 1
#   elif !defined(__has_include)
#       define INCLUDE_STD_FILESYSTEM_EXPERIMENTAL 1
#   elif __has_include(<filesystem>)
#       ifdef _MSC_VER
#           if __has_include(<yvals_core.h>)
#               include <yvals_core.h>
#               if defined(_HAS_CXX17) && _HAS_CXX17
#                   define INCLUDE_STD_FILESYSTEM_EXPERIMENTAL 0
#               endif
#           endif
#           ifndef INCLUDE_STD_FILESYSTEM_EXPERIMENTAL
#               define INCLUDE_STD_FILESYSTEM_EXPERIMENTAL 1
#           endif
#       else // #ifdef _MSC_VER
#           define INCLUDE_STD_FILESYSTEM_EXPERIMENTAL 0
#       endif
#   elif __has_include(<experimental/filesystem>)
#       define INCLUDE_STD_FILESYSTEM_EXPERIMENTAL 1
#   else
#       error Could not find system header "<filesystem>" or "<experimental/filesystem>"
#   endif
#   if INCLUDE_STD_FILESYSTEM_EXPERIMENTAL
#       include <experimental/filesystem>
namespace std {
	namespace filesystem = std::experimental::filesystem;
}
#   else
#       include <filesystem>
#   endif
#endif