Can't compile Postgres-6.5

Hello,
I've downloaded postgres-6.5 and tried to install on my Linux machine.
After I untarred, ran configure and make all, it seemed to pass through.

But at last I got the message:
ld -r -o SUBSYS.o fmgrtab.o adt/SUBSYS.o cache/SUBSYS.o error/SUBSYS.o
fmgr/SUBSYS.o hash/SUBSYS.o init/SUBSYS.o misc/SUBSYS.o mmgr/SUBSYS.o
sort/SUBSYS.o time/SUBSYS.o
make[2]: Leaving directory
`/home/postgres/postgresql-6.5/src/backend/utils'
gcc -o postgres access/SUBSYS.o bootstrap/SUBSYS.o catalog/SUBSYS.o
commands/SUBSYS.o executor/SUBSYS.o lib/SUBSYS.o libpq/SUBSYS.o
main/SUBSYS.o parser/SUBSYS.o nodes/SUBSYS.o optimizer/SUBSYS.o
port/SUBSYS.o postmaster/SUBSYS.o regex/SUBSYS.o rewrite/SUBSYS.o
storage/SUBSYS.o tcop/SUBSYS.o utils/SUBSYS.o ../utils/version.o -ldld
-lm -lbsd -ltermcap -lncurses  -export-dynamic
utils/SUBSYS.o: In function `handle_load':
utils/SUBSYS.o(.text+0x2ae35): undefined reference to `dlopen'
utils/SUBSYS.o(.text+0x2ae47): undefined reference to `dlerror'
utils/SUBSYS.o(.text+0x2aebc): undefined reference to `dlsym'
utils/SUBSYS.o: In function `load_file':
utils/SUBSYS.o(.text+0x2af5d): undefined reference to `dlclose'
utils/SUBSYS.o(.text+0x2afc7): undefined reference to `dlclose'
make[1]: *** [postgres] Error 1

I have no idea where those those required functions are.
Where can I fine those files?
My OS is Slackware 3.6 Linux 2.0.36.
My machine is PC ix586.

Thanks.

Paibool Prueksunand.