dlfcn.h?

Hi... I try to compile postgresql-6.4.2 in my Linux Slackware 3.2 but
when the compile try to do it  says (in the log file make.log)

.......
make[2]: Entering directory `/postgresql-6.4.2/src/backend/port'
gcc -I../../include -I../../backend   -O2  -Wall -Wmissing-prototypes
-I..   -c
dynloader.c -o dynloader.o
In file included from dynloader.c:24:
../../include/dynloader.h:19: dlfcn.h: No such file or directory
make[2]: *** [dynloader.o] Error 1
make[2]: Leaving directory `/postgresql-6.4.2/src/backend/port'
make[1]: *** [port.dir] Error 2
make[1]: Leaving directory `/postgresql-6.4.2/src/backend'
make: *** [all] Error 2

I try to find dlfcn.h in my system but it doesn't have....

It's someting wrong....

thanks for advanced