Add freebsd to goreleaser config

While at it, fixed the hook upx script to run per file, and ignore
binaries which are not supported.

scripts/upx.sh

@@ -2,6 +2,22 @@
 
 set -ex
 
-for dist_dir in ./dist/ctrld*; do
-  upx --brute "${dist_dir}/ctrld"
-done
+binary=$1
+
+if [ -z "$binary" ]; then
+  echo >&2 "Usage: $0 <binary>"
+  exit 1
+fi
+
+case "$binary" in
+  *_freebsd_*)
+    echo >&2 "upx does not work with freebsd binary yet"
+    exit 0
+    ;;
+  *_windows_arm*)
+    echo >&2 "upx does not work with windows arm/arm64 binary yet"
+    exit 0
+    ;;
+esac
+
+upx -- "$binary"