meson.build: install and search directories adjustments
This patch came in my mail from @catap:
Greetings,
I'd like to share with you a trivial patch which fixed work of knot-resolver when libknot installed under not expected path but it well announced via pkgconfig.
Unfortunately I can't create merge request via gitlab because I haven't got access not to fork, not to push to the main one.
Feel free to treat this patch under any comfotable lincse or public domain.
-- wbr, Kirill