portability: use -DGNULIB_POSIXCHECK.

portability: use -DGNULIB_POSIXCHECK.

Reported by Eric Blake.  See discussions at
<http://lists.gnu.org/archive/html/bug-bison/2009-09/msg00008.html>
and
<http://lists.gnu.org/archive/html/bug-gnulib/2009-10/msg00108.html>.
* HACKING (Release checks): Suggest -DGNULIB_POSIXCHECK.
* bootstrap.conf (gnulib_modules): Add all the printf modules
suggested by -DGNULIB_POSIXCHECK.  Add realloc-posix as
suggested by -DGNULIB_POSIXCHECK for gnulib's own vasnprintf.c.
(excluded_files): Remove m4/printf-posix.m4.
* tests/atlocal.in (LIBS): As for LDADD in src/local.mk, add
lib/libbison.a so gnulib libraries can be linked.