Replace freebsd-gnueabihf with freebsd

FreeBSD does not support GNU libc, so it makes no sense to use this
triple. Most likely previous builds were just using the FreeBSD libc
instead of gnueabihf. To fix this, we should just use
armv6-unknown-freebsd and armv7-unknown-freebsd triples. Note that
both of these are actually "soft-float", not "hard-float". FreeBSD has
never officially released hard-float arm32:

https://wiki.freebsd.org/ARMTier1