Today I wanted to upgrade Courier-Authlib from 0.63.0 and read this in the ChangeLog:

2010-03-06 Sam Varshavchik

* Remove the bundled libtdl library. Require the system-installed
libltdl library.

As expected, this gave me some problems with my old CentOS 5.9 release:

/bin/sh ./libtool –tag=CC –mode=link gcc -g -O2 -Wall -I.. -I./.. -export-dynamic -dlopen libauthuserdb.la -dlopen libauthpam.la -dlopen libauthshadow.la -dlopen libauthcustom.la -dlopen libauthpipe.la -o authdaemondprog authdaemond.o libltdl/libltdlc.la libcourierauthcommon.la liblock/liblock.la libhmac/libhmac.la md5/libmd5.la sha1/libsha1.la rfc822/libencode.la numlib/libnumlib.la -ldl
libtool: link: cannot find the library `libltdl/libltdlc.la’ or unhandled argument `libltdl/libltdlc.la’
make[2]: *** [authdaemondprog] Error 1
make[2]: Leaving directory `/usr/local/src/courier-authlib-0.65.0′
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/usr/local/src/courier-authlib-0.65.0′
make: *** [all] Error 2

I fixed this by adding this line to my build script (after configure):
sed -i -e 's/^LIBLTDL = ${top_build_prefix}libltdl\/libltdlc.la/LIBLTDL = -lltdl/' Makefile


Update, February 15th 2013: Today I found out that in a freshly installed VMware machine with CentOS 5.9, ltdl was missing. So I needed to add the following in my pre-build script as well:
rpm -q libtool-ltdl >/dev/null
if [ $? != 0 ]; then yum -q -y install libtool-ltdl; fi
rpm -q libtool-ltdl-devel >/dev/null
if [ $? != 0 ]; then yum -q -y install libtool-ltdl-devel; fi


Update, December 7th 2015: I wanted to build 0.66.4 today, and the problem reappeared. Luckily, I found this posting which saved me some time. Updated ‘sed’ command:
sed -i -e 's/^LIBLTDL = $(top_build_prefix)libltdl\/libltdlc.la/LIBLTDL = -lltdl/' Makefile