[CMake] Inserting a dependency before Qt moc is run

[Stephen Kelly]

Aurélien Gâteau wrote:

> I defined a custom command to generate the .json

Why a custom target? Wouldn't it make sense to generate the json file at 
CMake-configure time using execute_process? The desktop file is not 
generated.

If that is possible, it 'makes the problem go away'. 

However, I think there is something to be said for being able to specify 
dependencies of the autogen target. That's something for the -developers 
list though. I've pushed a commit for testing and review:

 http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=ae016fa8a

Thanks,

Steve.