Looks like -rpath is set no matter what for GNU/default host_os, ./configure line 7548. We may need to patch this. mowgli is configured as "internal" starting at/around line 10824. To solve this it just needs to find and be happy with the output of pkg-config. I'm guessing that having version 2.0-dev installed will be all that's needed for this to be set to "system".