portability: fix spawning on at least FreeBSD 8 and FreeBSD 9.

Reported by Johan van Selst at
<http://lists.gnu.org/archive/html/bug-bison/2010-03/msg00014.html>.
* NEWS (2.4.3): New.
* THANKS (Johan van Selst): Add.
* etc/prefix-gnulib-mk (prefix): Adjust regex for makefile
targets so that gnulib's new c++defs.h is matched.
* gnulib: Update to latest.
(cherry picked from commit 311b2e56ea)

Conflicts:

	NEWS

m4/.gitignore

@@ -131,8 +131,10 @@
 /warning.m4
 /warnings.m4
 /wchar.m4
+/wchar_h.m4
 /wchar_t.m4
 /wctype.m4
+/wctype_h.m4
 /wcwidth.m4
 /wint_t.m4
 /xalloc.m4