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This incorporates:
2019-02-24 nstrftime: support the ‘+’ flag
2019-02-24 stat, lstat: fix conflict with relocatable-prog-wrapper
2019-02-23 nstrftime: tweak arg order
2019-02-21 nstrftime: merge glibc strftime changes
2019-02-02 vla: add commentary about VLA_ELEMS
* build-aux/config.guess, doc/misc/texinfo.tex, lib/fstatat.c:
* lib/lstat.c, lib/nstrftime.c, lib/vla.h:
Copy from Gnulib.