* Honor CARGO_BUILD_TARGET in FreeBSD packaging for aarch64 release builds
Cross-built FreeBSD aarch64 archives were not possible: package.sh took the
arch from uname -m (the x86_64 VM host), built for the host, read binaries
from target/release, and ran the aarch64 gridcraft-cli to print its version.
When CARGO_BUILD_TARGET is set, build with --target, read from
target/<triple>/release, name the archive by the target's arch (aarch64 for
aarch64-unknown-freebsd, x86_64 otherwise), and skip running the binary.
Unset behavior is unchanged.
* Reject unsupported CARGO_BUILD_TARGET in FreeBSD packaging
Only x86_64-unknown-freebsd and aarch64-unknown-freebsd are valid; any other
value now fails before the build or packaging.
Dylan M. Taylor