Otherwise aacenc.o gets pulled in by the aacencdsp checkasm
test and it in turn pulls the rest of lavc in.
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
libavcodec as a DLL and this breaks checkasm because it links
both lavc and lavu statically.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>