Add upx to goreleaser builds

Reducing the size of the final binaries, except for darwin, where the
packed binaries failed to run.

.goreleaser.yaml

@@ -25,6 +25,8 @@ builds:
     gomips:
       - softfloat
     main: ./cmd/ctrld
+    hooks:
+      post: /bin/sh ./scripts/upx.sh
 archives:
   - format_overrides:
       - goos: windows

scripts/upx.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+set -ex
+
+for dist_dir in ./dist/ctrld*; do
+  upx --brute "${dist_dir}/ctrld"
+done