This reverts commit 2d4da30fde.
This Gnulib update was causing failures related to timezones in
stime.c. I tried to fix it by adopting the time_rz module from gnulib
but that then caused other failures. We can try again later.
* m4/gnulib-cache.m4: Use `dirfd'.
* libguile/filesys.c: Include Gnulib's <dirent.h> directly.
(dirfd): Remove. Suggested by Bruno Haible <bruno@clisp.org>.