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This incorporates:
2018-09-10 timespec: fix resolution confusion
2018-09-09 mktime: simplify in prep for glibc merge
2018-09-07 intprops: minor clarification of code
2018-09-06 stddef: Override max_align_t on NetBSD 8.0/x86
2018-09-06 fcntl: Fix F_DUPFD_CLOEXEC behaviour on Haiku
2018-09-06 strtoll, strtoull: Rely on limits-h module
2018-09-06 limits-h: Provide numerical limits macros
2018-09-06 fcntl: Don't access nonexistent optional argument
2018-09-02 mktime: fix unlikely race+overflow bug
2018-08-31 mktime, timegm: simplify glibc time64_t
2018-08-31 mktime, timegm: simplify merge to glibc
* build-aux/config.guess, build-aux/config.sub:
* lib/dtotimespec.c, lib/fcntl.c, lib/intprops.h:
* lib/limits.in.h, lib/mktime-internal.h, lib/mktime.c:
* lib/stat-time.h, lib/strtol.c, lib/timegm.c:
* lib/timespec-add.c, lib/timespec-sub.c, lib/timespec.h:
* lib/utimens.c, m4/limits-h.m4, m4/stddef_h.m4:
Copy from Gnulib.