pkg_check_modules gives both LIBUSB_LIBRARIES (bare names, -lusb-1.0) and
LIBUSB_LINK_LIBRARIES (absolute paths). Passing both links libusb twice,
and the bare name only resolves when libusb is in the default library
search path - which it is on Linux and is not under Homebrew on macOS,
where the link fails with "library not found for -lusb-1.0". The full
path alone is enough everywhere.
