system/coreutils: change in `pwd` behavior from 9.1 to 9.2 due to gnulib update

The following change in behavior was observed between coreutils release 9.1 and 9.2 in our development environment:

$ HERE=$(pwd) && (cd //tmp && for k in 9.1 9.2; do echo -n $k:\  && ${HERE}/coreutils-$k/src/pwd; done)
9.1: /tmp
9.2: //tmp

however it is not reproducible on a mostly-standard Ubuntu system:

$ HERE=$(pwd) && (cd //tmp && for k in 9.1 9.2; do echo -n $k:\  && ${HERE}/coreutils-$k/src/pwd; done)
9.1: /tmp
9.2: /tmp

This (coreutils) has been bisected to a gnulib bump, not a change in coreutils itself:

• https://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=commit;h=d42e4e9191abb818fc0e28507085a3945eed1477

The change in behavior is caused by:

• https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commit;h=356a414e8c15ef3f8cc7b7157427c8ce9a9f7c1b