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

diff -Nur cpl-6.1.1.orig/configure.ac cpl-6.1.1/configure.ac
--- cpl-6.1.1.orig/configure.ac	2012-06-04 18:38:01.000000000 +0100
+++ cpl-6.1.1/configure.ac	2012-06-04 22:14:23.000000000 +0100
@@ -60,8 +60,12 @@
 AC_ENABLE_STATIC(yes)
 AC_ENABLE_SHARED(yes)
 
-AC_LIBLTDL_CONVENIENCE
-AC_PROG_LIBTOOL
+LT_INIT([dlopen])
+AC_CHECK_HEADER([ltdl.h],
+    [AC_CHECK_LIB([ltdl], [lt_dladvise_init],
+        [LIBLTDL=-lltdl], [LIBLTDL=])],
+    [LIBLTDL=])
+
 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])
diff -Nur cpl-6.1.1.orig/Makefile.am cpl-6.1.1/Makefile.am
--- cpl-6.1.1.orig/Makefile.am	2012-06-04 18:38:01.000000000 +0100
+++ cpl-6.1.1/Makefile.am	2012-06-04 19:07:41.000000000 +0100
@@ -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 =