...and add both a static bash and busybox into the sandbox for building:
$ /nix/store/fz43jxs5qfg5vldzk38y2hmrcl58qk18-busybox-1.36.1/bin/sh -c 'declare -A foo'
/nix/store/fz43jxs5qfg5vldzk38y2hmrcl58qk18-busybox-1.36.1/bin/sh: declare: not found
The reason is that busybox's `sh` doesn't know about `declare` which
means it cannot build derivations with `__structuredAttrs = true;`.
Change-Id: Ie3ca431f862fd3e59dc649582704ae739ee5834a