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

build-aux/.cvsignore

@@ -1,5 +1,6 @@
 announce-gen
 arg-nonnull.h
+c++defs.h
 compile
 config.guess
 config.rpath

build-aux/.gitignore

@@ -1,5 +1,6 @@
 /announce-gen
 /arg-nonnull.h
+/c++defs.h
 /compile
 /config.guess
 /config.rpath