libxml2: pthread_join might be available without libpthread

contrib/src/libxml2/pthread.patch

+--- libxml2/configure.in.orig	2012-05-29 12:43:39.843757694 -0400
++++ libxml2/configure.in	2012-05-29 12:47:39.347755607 -0400
+@@ -913,12 +913,17 @@
+     echo Enabling multithreaded support
+     dnl Use pthread by default
+     if test "$with_threads" = "pthread" || test "$with_threads" = "" || test "$with_threads" = "yes" ; then
++        LIBS_saved="$LIBS"
+         AC_CHECK_HEADER(pthread.h,
+-	    AC_CHECK_LIB(pthread, pthread_join,[
+-	       THREAD_LIBS="-lpthread"
++        AC_SEARCH_LIBS(pthread_join, pthread,[
++	       THREAD_LIBS="$ac_cv_search_pthread_join"
++           if test "$THREAD_LIBS" = "none required"; then
++             THREAD_LIBS=""
++           fi
+ 	       AC_DEFINE([HAVE_LIBPTHREAD], [], [Define if pthread library is there (-lpthread)])
+ 	       AC_DEFINE([HAVE_PTHREAD_H], [], [Define if <pthread.h> is there])
+ 	       WITH_THREADS="1"]))
++        LIBS="$LIBS_saved"
+     fi
+     case $host_os in
+        *mingw32*) if test "$THREAD_LIBS" != "-lpthread"; then

contrib/src/libxml2/rules.mak

@@ -18,6 +18,7 @@ XMLCONF = --with-minimal --with-catalog --with-reader --with-tree --with-push --
 libxml2: libxml2-$(LIBXML2_VERSION).tar.gz .sum-libxml2
 	$(UNPACK)
 	$(APPLY) $(SRC)/libxml2/no-tests.patch
+	$(APPLY) $(SRC)/libxml2/pthread.patch
 	$(MOVE)
 
 .libxml2: libxml2