Namely ff_avg_h264_qpel8or16_hv1_lowpass_op_mmxext. It seems to exist
since 610e00b3594bf0f2a75713f20e9c4edf0d03a818 (a function like this
already existed before that commit, but it was static and
av_always_inline and was therefore not present in the actual binaries).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>