When I added the first copy of the CloudABI toolchain to the Ports tree,
I assumed that it would be easily possible to have a single Binutils
port that would support all of the architectures of interest. It seems
that this is not really supported, or simply awkward to use.
Let's just rename the cloudabi-binutils port to cloudabi-binutils-x86_64
and add an additional cloudabi-binutils-aarch64.