Win64 MinGW

[dsimcha]

I've just had the unexpected misfortune of having my work computer break, and
then the unexpected fortune of being told I'm getting an 8 core with 24 gigs
of RAM to replace it.  However, I strongly prefer Windows as my desktop OS.
Therefore, I've started caring a lot more lately about 64-bit Windows support.

How far away are we from getting a reasonably stable/usable MinGW GDC for
Win64?  I've noticed that GDC for Linux has made tremendous strides lately and
almost "just works" for the code I've been testing it on.  (Thanks to Iain for
his hard work.)  I've also noticed that GDC has been ported to Windows using
MinGW (thanks to Daniel Green), but as far as I can tell it only supports 32.
 Are there any major, fundamental roadblocks to 64 support or are we a few bug
fixes away?