configure.in: link with -lpthread when necessary

* configure.in: Explicitly add -lpthread to $LIBS.
With an empty "ACTION_IF_FOUND", AC_CHECK_LIB would have done
that for us automatically, but when there is an explicit third
argument, those commands are run instead of the default.
Reported by Jun Koi <junkoi2004@gmail.com>.

ChangeLog

+Fri Aug 22 10:30:42 CEST 2008 Jim Meyering <meyering@redhat.com>
+
+	configure.in: link with -lpthread when necessary
+	* configure.in: Explicitly add -lpthread to $LIBS.
+	With an empty "ACTION_IF_FOUND", AC_CHECK_LIB would have done
+	that for us automatically, but when there is an explicit third
+	argument, those commands are run instead of the default.
+	Reported by Jun Koi <junkoi2004@gmail.com>.
+
 Thu Aug 21 21:29:28 CEST 2008 Jim Meyering <meyering@redhat.com>
 
 	autobuild.sh: Fix minor shell-quoting bugs.

configure.in

@@ -90,6 +90,7 @@ AC_CHECK_HEADER([pthread.h],
 	[AC_CHECK_LIB([pthread],[pthread_join],[
 		AC_DEFINE([HAVE_LIBPTHREAD],[],[Define if pthread (-lpthread)])
 		AC_DEFINE([HAVE_PTHREAD_H],[],[Define if <pthread.h>])
+		LIBS="-lpthread $LIBS"
 	])])
 
 dnl Miscellaneous external programs.