[CMake] How to make INSTALL ( directory .... ) depend on other targets

[doob at gmx.de]

Hello,

how can I make an INSTALL( DIRECTORY .... ) target depend on another 
target FOO created with ADD_CUSTOM_TARGET to ensure the target gets 
build before installation.

I tried something like:

install( CODE "execute_process ( COMMAND make doc )" )

but oviously this is not independent of platform or generator.

The best thing would be an INSTALL option like the ALL option of

   ADD_CUSTOM_TARGET(Name [ALL] ...)

What I basicaly want to do is to install a directory with doxygen 
generated documentation. Maybe I'm totaly on the wrong direction.

Any sugestions?

regards

peter