Update from gnulib

Update from gnulib

This incorporates:
2016-09-07 flexmember: new macro FLEXALIGNOF
2016-09-07 flexmember: port better to GCC + valgrind
2016-08-18 Port modules to use getprogname explicitly
2016-09-02 manywarnings: add -fno-common
* admin/merge-gnulib (GNULIB_TOOL_FLAGS): Don’t avoid flexmember,
since time_rz now uses part of it.  Instead, remove m4/flexmember.m4.
* configure.ac (AC_C_FLEXIBLE_ARRAY_MEMBER): Define away,
since Emacs assumes C99 and therefore removes m4/flexmember.m4.
* lib/euidaccess.c, lib/group-member.c, lib/time_rz.c:
* m4/manywarnings.m4: Copy from gnulib.
* lib/flexmember.h: New file, from gnulib.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.