docker,worker: install g++-multilib

[ynezz]

(Moved over from https://gitlab.com/openwrt/buildbot/-/merge_requests/11) Cc @aloisklink

From openwrt/docker@5484951 (GitHub PR #89):

Node fails to cross-compile from a 64-bit build machine to 32-bit host with the following error:

  In file included from /usr/include/c++/8/memory:62,
  from ../deps/v8/src/libplatform/default-foreground-task-runner.h:8,
  from ../deps/v8/src/libplatform/default-foreground-task-runner.cc:5:
  /usr/include/c++/8/bits/stl_algobase.h:59:10: fatal error: bits/c++config.h:
    No such file or directory
  #include <bits/c++config.h>
          ^~~~~~~~~~~~~~~~~~
  compilation terminated.

On Debian, g++-multilib can be installed to fix this.

Fixes: https://github.com/openwrt/packages/issues/18476 Fixes: https://forum.openwrt.org/t/why-arent-the-node-and-node-npm-packages-available-on-arm-cortex-a9-vfpv3-d16-in-22-03-2/142722

[aparcar]

Please proceed