SWFDEC has been unmaintained for years, both in ports and upstream. On top of that, Flash Player is losing marketshare.
We can probably safely remove it from default options. This will also fix build on powerpc64 elfv2, which requires liboil (which is another abandonware that fails, per http://poudriere.rtk0.net/data/powerpc64-elfv2-pkubaj-pkubaj/2019-11-24_04h54m14s/logs/errors/liboil-0.3.17_3.log ).