I know that 64bit support on Windows is behind Linux etc for various reasons, but i thought i'd tried building some things with -m64 just to test, and got a bunch of errors like
std\file.d(223): Error: undefined identifier GetLastError std\file.d(2067): Error: undefined identifier WIN32_FIND_DATA Which appears to be because various things in Phobos use version(Win32), and only 'Win64' is set in 64bit builds. I guess that at least some of these should be using version(Windows) instead?