build: update to latest gnulib

Included in this are gnulib changes 3ea43e02 2768ceb7
which make the device IDs from /proc/self/mountinfo
available to df.  This can be leveraged by a subsequent
change to df to present a more accurate list of file systems.

* bootstrap: Merge from gnulib.
* src/ls.c (dev_ino_pop): s/obstack_blank/obstack_blank_fast/
as this API/ABI has changed, giving memory exhausted errors
if negative (large positive) numbers are passed to obstack_blank().
* tests/df/skip-duplicates.sh: Adjust as the new gnulib code
requires a non NULL mnt_opts even when mnt_type is not "none".
tests: fix possible 8 minute running time of inotify-rotate.sh

Commit v8.23-63-g111a2b9 removed the expensive tag on this test,
as it runs quickly on systems with inotify.  However without that
it would take about 8 minutes for the test to complete all iterations.

* tests/tail-2/inotify-rotate.sh: Tag as expensive without inotify.
Also adjust the polling parameters used on systems without inotify
so that the test completes within about 15 seconds.