* Otherwise, they pull compilation of xpp tools via implicit rules.
* This breaks build without libusb/libusbx
* To test this scenario:
    ./configure .... --without-libusb --without-libusbx
Signed-off-by: Oron Peled <oron.peled@xorcom.com>
Signed-off-by: Russ Meyerriecks <rmeyerriecks@digium.com>