それぞれ微妙に主張が違う気がす
https://gist.github.com/repeatedly/2470712
https://dlang.org/dmd-windows.html (-m64)
http://wiki.dlang.org/Installing_DMD_on_64-bit_Windows_7_(COFF-compatible)
http://www.ku6.jp/report/65.html
http://stackoverflow.com/questions/2376816/how-well-does-d-support-64-bit