Neither --buildtype=plain nor --buildtype=debug set -ffast-math, so
llround() is kept as a function call and isn’t optimised out into
cvttsd2siq (on amd64), thus requiring the math lib to be linked.
Note that even with -ffast-math, it isn’t guaranteed that a call to
llround() will always be omitted (I have reproduced this on PowerPC), so
this fix is correct even if we ever decide to enable -ffast-math in
other build types.
Upstream libplacebo added support for dav1d integration directly,
allowing us to vastly simplify all of this code. In order to take
advantage of new optimizations, I had to allow update_frame to unref the
Dav1dPicture. (This is fine, since double unref is a no-op)
In addition, some of the functions we use were deprecated in recent
libplacebo versions, so since we're taking a new dependency we might as
well fix the deprecation warnings.
Henrik Gramner