[Cmake] custom commands and libraries

[Doug Henry]

In the mastering cmake book I found the section on generating files
using the ADD_CUSTOM_COMMAND and ADD_CUSTOM_TARGET commands.  In my
project I first build a generator executable that is then run on various
xml files to create source code.  This all works as described in the
book.  However, I would like to add the generated files to ADD_LIBRARY
so that they are built after generation.  Is that possible?  Adding the
filenames to ADD_LIBRARY does not cause the custom commands to be
called, I assume there is some way to trigger such a thing to happen,
but I missed or overlooked it in the documentation.

thanks