xbps-src: make-repoidx failed for repos with only noarch pkgs.

xbps-src/xbps-src.sh.in

@@ -402,6 +402,8 @@ make-repoidx)
 	fi
 	echo "=> Updating package index for local repository at"
 	echo "   $XBPS_PACKAGESDIR..."
+	[ ! -d "$XBPS_PACKAGESDIR/$(uname -m)" ] && \
+		mkdir -p "$XBPS_PACKAGESDIR/$(uname -m)"
 	${XBPS_REPO_CMD} genindex ${XBPS_PACKAGESDIR} 2>/dev/null
 	[ $? -eq 0 ] && echo "=> done."
 	;;