The patched meson.build for dav1d just changes the include_directories
from 'include/dav1d' to 'include' and, while we're at it, removes the
pkg_config stuff to avoid a deprecation warning.
AV1 decoding is pretty broken in upstream ffms2, so point the wrap to a
fork that has some hack patches for it. BestSource works fine out of the
box, though.
