Please note this is a simple description of linking behaviours: for more detailed instructions see more appropriate documentation regarding automatic or manual installations.
Linking of qmail-smtpd patched with chkuser 2.0 is extremely easy, because all is solved by the patch.
qmail libraries
No particular need over existing qmail objects and libraries.
Unique note: as shown in next paragraph, in Makefile dns.lib is added to qmail-smtpd building instructions: so, if you did previously patch qmail-smtpd in order to include dns.lib, take care to delete the duplication from those lines.
vpopmail dependencies
In order to link the right vpopmail libraries, with the appropriate libraries on which vpopmail relies, Makefile is modified with the inclusion of these (bold) lines:
# Don't edit Makefile! Use conf-* for configuration.
VPOPMAIL_HOME=/home/vpopmail
SMTPD_CHKUSER_OBJ=chkuser.o dns.o
VPOPMAIL_LIBS=`head -1 $(VPOPMAIL_HOME)/etc/lib_deps` `cat dns.lib`
SHELL=/bin/sh
where the file /home/vpopmail/etc/libs_dep is used to learn which libraries must be linked.
This semplifies radically every installation, as the patch is automatically compatible with every cbd, MySQL, LDAP, PostgreSQL or other database used by vpopmail.