Add builduser to same groups as on host

This prevents permission errors when relying on a user's group
for accessing certain files (made available within the container
via bind mounts).

arch-nspawn.in

@@ -127,7 +127,9 @@ eval "$(grep -a '^CARCH=' "$working_dir/etc/makepkg.conf")"
 
 [[ -z $nosetarch ]] || unset CARCH
 
-exec systemd-nspawn -q \
+for p in  echo exec; do
+[[ $p == echo ]] && msg "Entering chroot \"$working_dir\" via:"
+"$p" systemd-nspawn -q \
 	-D "$working_dir" \
 	-E "PATH=/usr/local/sbin:/usr/local/bin:/usr/bin" \
 	--register=no \
@@ -136,3 +138,4 @@ exec systemd-nspawn -q \
 	--resolv-conf=copy-host \
 	"${mount_args[@]}" \
 	"$@"
+done

makechrootpkg.in

@@ -159,6 +159,7 @@ prepare_chroot() {
 	local builduser_uid builduser_gid
 	builduser_uid="$(id -u "$makepkg_user")"
 	builduser_gid="$(id -g "$makepkg_user")"
+	builduser_gids="$(id -G "$makepkg_user")"
 	local install="install -o $builduser_uid -g $builduser_gid"
 	local x
 
@@ -167,6 +168,12 @@ prepare_chroot() {
 	# an x86_64 host).
 	sed -e '/^builduser:/d' -i "$copydir"/etc/{passwd,shadow,group}
 	printf >>"$copydir/etc/group"  'builduser:x:%d:\n' "$builduser_gid"
+	for gid in $builduser_gids; do
+		if [[ $gid != $builduser_gid ]]; then
+			group_name=$(getent group "$gid" | cut -d: -f1)
+			printf >>"$copydir/etc/group"  "$group_name:x:%d:builduser\n" "$gid"
+		fi
+	done
 	printf >>"$copydir/etc/passwd" 'builduser:x:%d:%d:builduser:/build:/bin/bash\n' "$builduser_uid" "$builduser_gid"
 	printf >>"$copydir/etc/shadow" 'builduser:!!:%d::::::\n' "$(( $(date -u +%s) / 86400 ))"