Merge from Gnulib
This incorporates:
2018-01-05 maint: Add encoding marker for Emacs to non-ASCII sources
2018-01-04 update-copyright: Handle use of ©
2018-01-04 pthread_sigmask: Avoid compilation error on mingw
2018-01-02 stat-time: silence -Wunused-parameter regression
* build-aux/config.guess, build-aux/config.sub:
* build-aux/update-copyright, doc/misc/texinfo.tex, lib/gnulib.mk.in:
* lib/md5.c, lib/md5.h, lib/sha1.c, lib/sha1.h, lib/sha256.c:
* lib/sha256.h, lib/sha512.c, lib/sha512.h, lib/signal.in.h:
* lib/stat-time.h: Copy from Gnulib, or regenerate.
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