There are cases where a package is known to dpkg due to Provides
or Suggests, but where it's not installed and where we don't want to
generate a broken Built-Using entry.

I recently had the case on arm64 where u-boot-rockchip is not installed
but where it would still generate an entry:

  ./build/util/write-built-using
  dh_gencontrol
  dpkg-gencontrol: warning: can't parse dependency u-boot-rockchip (= )