Otherwise checkasm/vf_bwdif.c pulls in vf_bwdif.c and
then all of libavfilter. Besides being bad size-wise
this also has the downside that it pulls in
avpriv_(cga|vga16)_font from libavutil which are marked
as being imported from another library when building
libavfilter as a DLL and this breaks checkasm because
it links both lavfi and lavu statically.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>