ffmpeg: update to 3.4.2.
ffmpeg: update to 3.4.2.

Closes: #11579 [via git-merge-pr]

NeoChontrix/void-packages,necrophcodr/void-packages,coredumb/void-packages,necrophcodr/void-packages,NeoChontrix/void-packages,NeoChontrix/void-packages,coredumb/void-packages,coredumb/void-packages,coredumb/void-packages,coredumb/void-packages,necrophcodr/void-packages,coredumb/void-packages,NeoChontrix/void-packages,NeoChontrix/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,NeoChontrix/void-packages