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This incorporates:
2020-09-05 verify: avoid __builtin_assume
2020-08-30 strerrorname_np: New module
2020-08-26 include_next, stdint, time_rz: Change configure message
* lib/gnulib.mk.in: Regenerate.
* lib/string.in.h, lib/verify.h, m4/include_next.m4, m4/stdint.m4:
* m4/string_h.m4, m4/time_rz.m4: Copy from Gnulib.