The ARM release builds require u-boot, and u-boot's build infrastructure (for at least certain versions) is hardcoded to use a host gcc. This is currently handled by explicitly building and installing in gnu/usr.bin/cc but this will not be possible once gcc 4.2.1 is removed from the source tree. I suspect u-boot is just building some basic host tools and it may be possible to just make a symlink cc -> gcc in the chroot for the builds. See also https://reviews.freebsd.org/D1317
The mechanism for building u-boot for ARM images is transitioning towards ports/packages as the build mechanism. See sysutils/u-boot-beaglebone and other u-boot-* ports.
I just stumbled across this. We're completely converted to using u-boot ports now, right? Does that mean the changes to release.sh to pre-build gperf should be reverted? And should this PR be closed as OBE?
Rework by gjb in r282553 seems to have addressed this.