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This incorporates:
2019-10-23 nstrftime: speed up integer overflow checking
2019-10-23 port better to GCC under macOS
2019-10-15 inttypes: use more-robust test for int range
2019-10-14 update-copyright: use en dashes in .texi ranges
* build-aux/update-copyright, lib/intprops.h, lib/inttypes.in.h:
* lib/nstrftime.c, lib/verify.h:
Copy from Gnulib.