[CMake] Install optional targets

[Stephen Kelly]

Tim Gallagher wrote:

> Hi,
> 
> I asked about this awhile back and haven't had any luck with it, so I'll
> try again.
> 
> What we are trying to do is have a project (called Utilities) that has a
> bunch of targets (the actual utility executables). Let's say there are 4
> utils: pre, post, grid, and restart. We would like to do something like:
> 
> make pre
> make post
> make install
> 
<snip>

> Any suggestions?
> 

KDE uses macro_optional_add_subdirectory(grid) for this.

http://quickgit.kde.org/index.php?p=extra-cmake-
modules.git&a=blob&h=e1733bcce714c216bd253420ea0a37f5bd1ba68b&hb=f0937a4fe5db2ab7f566110876d2984779f33a3e&f=modules/ECMOptionalAddSubdirectory.cmake

According to the notes

http://community.kde.org/KDE_Core/Platform_11/Buildsystem/FindFilesSurvey

this won't be accepted into CMake. If you like that idea better than what 
you currently have you can copy the file. We'll be making releases of extra-
cmake-modules eventually.

All the best,

Steve.