The Slackware Qt package includes full source.  If you're looking for the
latest official source tar archive, try:

ftp://ftp.troll.no/

To build as supplied by Slackware:

cd /usr/lib/qt
make clean
make linux-g++-shared
move manpages into /usr/man
move libs into /usr/lib
chmod 755 bin/qtrename140
make sure the install script from the binary package is in place, the two
scripts are in /etc/profile.d, and the sections that will be rebuilt by
makepkg (the include links) are edited out.