By now, the port builds without any multilib enabled.
In particular, usual Cortex-M devices require a fine-grained multilib setup though, as they ship with plenty different features.
The diff creates options to build the port without multilib, with a default multilib set, or with multilib sets optimized for either Cortex-A, or Cortex-R/M devices. All these options are already offered by the underlying GCC source, but they are not accessible within the FreeBSD ports.