[CMake] getting the right set of Qt libraries

[Tyler Roscoe]

As noted in the other question I just posted, I'm collecting all my 3rd
party dependencies into one place so my application is self-contained.

I'm using FindQt4 to manage the Qt stuff. FindQt4 has some clever logic
where each buildable unit that uses Qt can define the Qt submodules it
needs:

set (QT_USE_QTOPENGL 1)
set (QT_USE_QTUITOOLS 1)
etc.

This system is nice because it means that a buildable only links against
the Qt libs it needs, rather than linking against all 138314 individual
Qt libraries every time.

How do you guys insure that you have all the required libraries? I
assume you're parsing ${QT_LIBRARIES} and copying each of those to your
final destination.

But let's say my main top-level executable only needs the Qt core lib,
while several of the libraries that the executable depends on need QtXml
or QtOpenGl or whatever? 

Do you just set all the QT_USE_* for all the submodules at the top level
and make all of your buildables link against all these Qt submodules? 

Do you have some magic where each buildable sets QT_USE_* for the
submodules it uses but then registers each of these submodules at the
top-level so the top-level application can know which libraries it needs
to copy to the destination directory? 

Something else?

Hopefully this question makes sense. I'm again looking for The CMake Way
to handle this scenario.

Thanks,
tyler