Help with Win64 port

[George Brewster]

Hey,
I'd really like to see ghc working on 64-bit Windows, so I've decided to
take at least a quick stab at getting it going.
Having talked to some of the people on #ghc, it sounds like the first
thing to do is get an unregisterised build going, which sounded like it
may be managable. So to that end, I've pulled the 6.12 branch, done a
32-bit build, changed the build config to do an unregisterised build and
turn off the native code generator, found a version of mingw64 which
seems to work for me, stuffed it in in place of the in-tree mingw, and
got my build to fail.

At this point, I'd like to get a general idea of what my strategy should
be. I read the Building/Porting page on the wiki, and used the config
file there as an example of how to do an unregisterised build, but have
been ignoring anything related to the hc file bootstrapping process, as
I have a working ghc on my platform, just of the wrong bitness.

In particular, if there are any changes that you know I'll need to make
to the source to get this working, please let me know. The more of those
I learn about now, the less fumbling around I'll have to do as things
break. In particular, is there some place where I indicate that I'm
build a 64-bit compiler? I didn't find anything with a quick look.

I have very little time to work on it, and no familiarity with ghc
internals, so I wouldn't expect much, but I'm hoping I can get it going...

-George