bsd.port.mk is portmgr territory (via the GNATS Auto Assign Tool)
I don't see why we need this, our Linux support is 32-bit even on amd64 and we
don't have 64-bit Linux support at all.
While this is a patch for bsd.port.mk, this is more emulation@ territory.
I can see a usecase for this by the time we get around to implementing architectures other than the currently supported i386/x86_64 in the Linuxulator.