[CMake] How to associate a command with a auto-generated target?

[Alexander Neundorf]

On Monday 10 November 2008, Óscar Fuentes wrote:
> I wish to execute a command when the `clean' target is invoked. That is,
> my command shall execute on addition of the normal target action.

Doesn't work, you have to do it the other way round: create a custom target 
my-special-clean, do what you need, and also execute something like 
${CMAKE_MAKE_COMMAND} <directories etc> clean

Alex