rebranding a i386 binary to be a amd64 binary

[Aryeh Friedman]

Even though I know this is asking for it I want to test the new nVidia
driver on amd64 and the only issue with a hand compile (from nVidia's
tar not the ports one) is src/nv-kernel.o is branded elf-i386-32 and
amd64 wants it branded elf-amd64-64.  This file comes from them as a
precompiled object so rebranding seems to be my only option.