Merge from gnulib

Merge from gnulib

This incorporates:
2017-09-08 stddef: Avoid conflict with system-defined max_align_t
2017-08-24 warnings: fix compilation with old autoconf
2017-08-23 glob: merge from glibc with Zanella glob changes
2017-08-17 random: Fix test compilation failure on Cygwin 1.5.25
* doc/misc/texinfo.tex, lib/flexmember.h, lib/stddef.in.h:
* lib/stdlib.in.h, m4/manywarnings.m4, m4/stdlib_h.m4:
* m4/warnings.m4:
Copy from Gnulib.
* lib/gnulib.mk.in: Regenerate.