Merge from gnulib

Merge from gnulib

This incorporates:
2017-05-01 New module 'localtime-buffer'
2017-04-30 utimens: Add support for native Windows
* admin/merge-gnulib (AVOIDED_MODULES): Add tzset.
* configure.ac (tzset): No need for Emacs itself to check now.
* lib/gettimeofday.c, lib/time.in.h, lib/time_rz.c, lib/utimens.c:
* m4/gettimeofday.m4, m4/time_h.m4, m4/time_rz.m4: Copy from gnulib.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
* lib/localtime-buffer.c, lib/localtime-buffer.h:
* m4/localtime-buffer.m4: New files, copied from gnulib.
* src/editfns.c (init_editfns): Assume tzset is callable.