fix PYTHON_LIBS

on some platforms there are extra libs needed when linking with -lpython,
for example -pthread and -lutil on OpenBSD

configure.in

@@ -4489,8 +4489,9 @@ elif test -n "$with_system_python" -o -n "$with_system_libs" && \
 
    python_include=`$PYTHON -c "import distutils.sysconfig; print distutils.sysconfig.get_config_var('INCLUDEPY');"`
    python_version=`$PYTHON -c "import distutils.sysconfig; print distutils.sysconfig.get_config_var('VERSION');"`
+   python_libs=`$PYTHON -c "import distutils.sysconfig; print distutils.sysconfig.get_config_var('LIBS');"`
    PYTHON_CFLAGS="-I$python_include"
-   PYTHON_LIBS="-lpython$python_version"
+   PYTHON_LIBS="-lpython$python_version $python_libs"
 fi
 if test "$with_system_python" = "yes" ; then
    SYSTEM_PYTHON=YES