In general, the man page for the symbol you can't find tells you 
	what libraries you need to link in. 

man dlsym
	Link with -ldl.

DLSYM(3)                                         Linux Programmer's Manual                                        DLSYM(3)

NAME
       dlsym, dlvsym - obtain address of a symbol in a shared object or executable

SYNOPSIS
       #include <dlfcn.h>

       void *dlsym(void *handle, const char *symbol);

       #define _GNU_SOURCE
       #include <dlfcn.h>

       void *dlvsym(void *handle, char *symbol, char *version);

       Link with -ldl.