use system libtdl from libtool instead of bundled one
see http://www.flameeyes.eu/autotools-mythbuster/libtool/plugins.html
bicatali@gentoo.org

--- cpl-7.0.orig/configure.ac	2012-06-04 18:38:01.000000000 +0100
+++ cpl-7.0/configure.ac	2012-06-04 22:14:23.000000000 +0100
@@ -60,8 +60,9 @@
 AC_ENABLE_STATIC(yes)
 AC_ENABLE_SHARED(yes)
 
-AC_LIBLTDL_CONVENIENCE
-AC_PROG_LIBTOOL
+LT_INIT([dlopen])
+LT_CONFIG_LTDL_DIR([libltdl])
+AC_LIB_LTDL
 AC_SUBST(INCLTDL)
 AC_SUBST(LIBLTDL)
 AC_SUBST(LIBTOOL_DEPS)
@@ -131,7 +135,6 @@
 CPL_CONFIG_FUNC
 
 # Configure subpackages
-AC_CONFIG_SUBDIRS(libltdl)
 
 if test ! x$"cpl_cv_with_system_cext" = xyes; then
         AC_CONFIG_SUBDIRS([libcext])
--- cpl-7.0.orig/Makefile.am
+++ cpl-7.0/Makefile.am
@@ -25,11 +25,10 @@
 DISTCLEANFILES = *~
 
 if GASGANO_SUPPORT
-libltdl = libltdl
 cpljava = cpljava
 endif
 
-SUBDIRS = $(libltdl) $(libcext) cplcore cplui cpldrs cpldfs $(cpljava)
+SUBDIRS = $(libcext) cplcore cplui cpldrs cpldfs $(cpljava)
 
 HTML_SUBDIRS =