golang: Move module cache into DL_DIR

This also adds a config option GOLANG_MOD_CACHE_WORLD_READABLE; if
enabled, chmod is run after a Go package build to make all
files/directories in the module cache world-readable.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

lang/golang/golang-build.sh

@@ -0,0 +1,48 @@
+#!/bin/sh
+
+log() {
+	# shellcheck disable=SC2039
+	local IFS=" "
+	printf '%s\n' "$*"
+}
+
+log_error() {
+	# shellcheck disable=SC2039
+	local IFS=" "
+	printf 'Error: %s\n' "$*" >&2
+}
+
+cache_cleanup() {
+	if ! [ -d "$GO_MOD_CACHE_DIR" ]; then
+		return 0
+	fi
+
+	# in case go is called without -modcacherw
+	find "$GO_MOD_CACHE_DIR" -type d -not -perm -u+w -exec chmod u+w '{}' +
+
+	if [ -n "$CONFIG_GOLANG_MOD_CACHE_WORLD_READABLE" ]; then
+		find "$GO_MOD_CACHE_DIR"      -type d -not -perm -go+rx -exec chmod go+rx '{}' +
+		find "$GO_MOD_CACHE_DIR" -not -type d -not -perm -go+r  -exec chmod go+r  '{}' +
+	fi
+
+	return 0
+}
+
+
+if [ "$#" -lt 1 ]; then
+	log_error "Missing command"
+	exit 1
+fi
+
+command="$1"
+shift 1
+
+case "$command" in
+	cache_cleanup)
+		cache_cleanup
+		;;
+	*)
+		log_error "Invalid command \"$command\""
+		exit 1
+		;;
+esac