Update from gnulib

Update from gnulib

This incorporates:
2020-01-10 fix major regression from 2020-01-04
2020-01-05 tests: avoid GCC over-optimization
2020-01-04 fix AC_CHECK_DECL so it deactivates clang's built-ins
2020-01-03 getopt-posix: fix compilation failure in testdirs
2020-01-03 doc: mention the 64-bit inode number problem
2020-01-02 wchar: make the HP-UX workaround work on HP-UX 11.31
* build-aux/config.guess, build-aux/config.sub, lib/inttypes.in.h:
* lib/stdlib.in.h, lib/unistd.in.h, m4/00gnulib.m4, m4/largefile.m4:
* m4/unistd_h.m4: Copy from Gnulib
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.