multimedia/ffmpeg: update to 4.0

• FFSERVER support was removed upstream
• libressl now uses libtls backend instead of patching openssl one
• Clang i386 no longer uses 16-byte aligned stack

Changes: https://git.ffmpeg.org/gitweb/ffmpeg.git/blob/n4.0:/Changelog
ABI: https://abi-laboratory.pro/tracker/timeline/ffmpeg/
PR: 227726
Exp-run by: antoine
Differential Revision: https://reviews.freebsd.org/D15175