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.

m4/.gitignore

@@ -1,18 +1,28 @@
 /00gnulib.m4
 /absolute-header.m4
+/alloca.m4
 /argmatch.m4
 /assert.m4
 /config-h.m4
 /dirname.m4
 /dos.m4
 /double-slash-root.m4
+/dup2.m4
 /environ.m4
 /errno_h.m4
 /error.m4
 /exitfail.m4
+/exponentd.m4
+/exponentf.m4
+/exponentl.m4
 /extensions.m4
 /fcntl_h.m4
+/float_h.m4
 /fopen.m4
+/fpieee.m4
+/fprintf-posix.m4
+/frexp.m4
+/frexpl.m4
 /getopt.m4
 /getpagesize.m4
 /gettext.m4
@@ -25,11 +35,16 @@
 /include_next.m4
 /inline.m4
 /intlmacosx.m4
+/intmax_t.m4
 /inttypes-h.m4
 /inttypes-pri.m4
 /inttypes.m4
+/isnand.m4
+/isnanf.m4
+/isnanl.m4
 /javacomp.m4
 /javaexec.m4
+/ldexpl.m4
 /lib-ld.m4
 /lib-link.m4
 /lib-prefix.m4
@@ -39,6 +54,7 @@
 /locale-zh.m4
 /longlong.m4
 /malloc.m4
+/math_h.m4
 /mbrtowc.m4
 /mbsinit.m4
 /mbstate_t.m4
@@ -47,11 +63,22 @@
 /mmap-anon.m4
 /multiarch.m4
 /nls.m4
+/nocrash.m4
 /po.m4
+/printf-frexp.m4
+/printf-frexpl.m4
+/printf-posix-rpl.m4
+/printf-posix.m4
+/printf.m4
 /progtest.m4
 /quote.m4
 /quotearg.m4
+/realloc.m4
 /setenv.m4
+/signbit.m4
+/snprintf-posix.m4
+/snprintf.m4
+/sprintf-posix.m4
 /stdbool.m4
 /stddef_h.m4
 /stdint.m4
@@ -71,6 +98,12 @@
 /unistd-safer.m4
 /unistd_h.m4
 /unlocked-io.m4
+/vasnprintf-posix.m4
+/vasnprintf.m4
+/vfprintf-posix.m4
+/vsnprintf-posix.m4
+/vsnprintf.m4
+/vsprintf-posix.m4
 /warning.m4
 /warnings.m4
 /wchar.m4