allows to set PYLIBDIR externally

git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@7300 626c5289-ae23-0410-ae9c-e8d60b6d4f22

configure.in

@@ -555,7 +555,7 @@ if test -n "$PYTHON"; then
     # Find the directory for libraries this is necessary to deal with
     # platforms that can have apps built for multiple archs: e.g. x86_64
     AC_MSG_CHECKING(for Python lib dir)
-    PYLIBDIR=`($PYTHON -c "import sys; print sys.lib") 2>/dev/null`
+    PYLIBDIR?=`($PYTHON -c "import sys; print sys.lib") 2>/dev/null`
     if test -z "$PYLIBDIR"; then
       # older versions don't have sys.lib  so the best we can do is assume lib
       PYLIBDIR="lib"