[BUILD] remove gen dir before regenerating it
[BUILD] remove gen dir before regenerating it

Change-Id: Ib6bcacab93016da8e554346575bcbcaf254deedb
Reviewed-on: https://gerrit.parrot.biz/29173
Reviewed-by: Maxime Maitre <e46fe1f9761923e97d4fbff83ab76adb16770b5c@parrot.com>

Parrot-Developers/libARController,Parrot-Developers/libARController,Parrot-Developers/libARController,Parrot-Developers/libARController