docker,worker: install gcc-mulitlib

docker,worker: install gcc-mulitlib

From openwrt/docker[1]:

This is required for luajit, which is in packages feed.  While it works
fine for ARMv8 (tested by using Github Actions: aarch64_cortex-a53) and
x84_x64 (tested inside Docker container, it does not work for 32-bits
target and because of that we need to install gcc-multilib.

Luajit fails with the following output: (tested against target:
	arm_cortex-a9+vfpv3-d16_musl_eabi inside Docker SDK image)

/usr/include/limits.h:26:10: fatal error: bits/libc-header-start.h: No
such file or directory #include <bits/libc-header-start.h>
^~~~~~~~~~~~~~~~~~~~~~~~~~

[1]: https://github.com/openwrt/docker/pull/74/commits/f9da188d53fd9809ca4911089611e1f42422d049

Signed-off-by: Paul Spooren <mail@aparcar.org>