[Cmake] Adding generated files to "clean" target ?

[Jean-Francois LECOMTE]

Hi,

I've written a plugin which can now automatically generate *.c files
from specific interface definition files (*.xwi ) files and use them in
any EXECUTABLE or LIBRARY.

I found no way to add this generated files in the clean target. 
I've seen GENERATED_QT_FILES are hardcoded in OutputMakeRule for clean
target in cmake code.

Is there any way to add my own generated file to the clean target using
the CAPI.

I can add a POSTBUILD command for my own target, but in this way
generated files are always removed.

Thanks.