Libtool 2.2.2 requires this is used with AC_SUBST

RP - 14/4/08

--- /tmp/configure.in	2008-06-02 15:21:22.254641651 +0200
+++ fontconfig-2.4.1/configure.in	2008-06-02 15:21:48.485061892 +0200
@@ -46,6 +46,7 @@
 AC_SUBST(LT_CURRENT)
 AC_SUBST(LT_REVISION)
 LT_AGE=1
+AC_SUBST(LT_AGE)
 
 LT_VERSION_INFO="$LT_CURRENT:$LT_REVISION:$LT_AGE"
 AC_SUBST(LT_VERSION_INFO)