This package installs also static libs ".a" please provide do add relative USE. TIA /usr/lib/libusb.a /usr/lib/libusbpp.a /usr/lib/libusbpp-0.1.so.4.4.4 /usr/lib/libusbpp.la /usr/lib/libusb.so /usr/lib/pkgconfig/libusb.pc /usr/lib/libusbpp.so /usr/lib/libusbpp-0.1.so.4 /usr/lib/libusb.la /usr/lib/libusb-1.0.a /usr/lib/libusb-1.0.so.0.0.0 /usr/lib/pkgconfig/libusb-1.0.pc /usr/lib/libusb-1.0.la /usr/lib/libusb-1.0.so /usr/lib/libusb-1.0.so.0 Please remove also .la if is not needed.
http://sources.gentoo.org/dev-libs/libusb/libusb-1.0.8.ebuild?r1=1.10&r2=1.11