`env -u` is not supported by the system `env` utility on AIX.
`/opt/freeware/bin/env` is the standard path for the GNU coreutils `env`
utility as distributed by the AIX Toolbox for Open Source Software.
Adding `/opt/freeware/bin` to `PATH` causes issues by picking up other
utilities that are less capable, in an AIX context, than the system
ones.
This patch modifies the relevant usage of `env` to use (on AIX) the full
path to `/opt/freeware/bin/env`.