AMD64 port

[Simon 'corecode' Schubert]

Matthew Dillon wrote:
    This does bring up an issue which I think we want to resolve for
    this release, which is to build a GCC that supports both 32 and 64 bit
    targets (even if the OS doesn't, yet).  I'll look into that.
    Our buildworld will build a cross-platform GCC based on TARGET_PLATFORM
    and our buildkernel will then use it, theoretically, but it definitely
    isn't as convenient as having all the support built into GCC in the
    first place.
However, there is not much point in that unless you also build some libraries, at least libgcc.a.  And for those we'd need the right kernel headers.

Plus, what's the gain?  I can see the use on a 64 bit system, however.

cheers
 simon