gistfile1.txt

$ ./configure --prefix=/usr/local/collectd --without-included-ltdl
checking build system type... i386-unknown-freebsd7.2
checking host system type... i386-unknown-freebsd7.2
checking for gcc... gcc

blah blah blah

checking whether libtool supports -dlopen/-dlpreopen... yes
checking for ltdl.h... no
checking where to find libltdl headers... -I${top_srcdir}/libltdl
checking where to find libltdl library... ${top_build_prefix}libltdl/libltdlc.la

gistfile2.txt

$ ./configure --prefix=/usr/local/collectd --without-included-ltdl --with-ltdl-include=/usr/local/include --with-ltdl-lib=/usr/local/lib --disable-static

blah blah blah

checking whether libtool supports -dlopen/-dlpreopen... yes
checking for ltdl.h... no
checking where to find libltdl headers... -I/usr/local/include
checking where to find libltdl library... -L/usr/local/lib -lltdl

$ make
Making all in libltdl
/bin/sh /home/foo/src/collectd-4.9.1/libltdl/config/install-sh -d .
cp ./argz_.h argz.h-t
mv argz.h-t argz.h
make  all-am
/bin/sh ./libtool  --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I.  -DLT_CONFIG_H='<config.h>' -DLTDL -I. -I.  -Ilibltdl -I./libltdl -I./libltdl   -g -O2 -MT dlopen.lo -MD -MP -MF .deps/dlopen.Tpo -c -o dlopen.lo `test -f 'loaders/dlopen.c' || echo './'`loaders/dlopen.c

...

make: don't know how to make -L/usr/local/lib. Stop