[RFA] Add support for 64bit Windows

[Joel Brobecker]

> 2009-01-10  Joel Brobecker   <brobecker@adacore.com>
> 
>         * amd64-windows-nat.c, amd64-windows-tdep.c: New files.
>         * config/i386/mingw64.mh, config/i386/nm-cygwin64.h: New files.
>         * configure.host, configure.tgt: Add handling for x86_64/windows.
>         * config/djgpp/fnchange.lst: Add entries for amd64-windows-nat.c
>         and amd64-windows-tdep.c.

Now checked in :).

-- 
Joel