Revision 483320

MFH: r482030 r482658 r482928 r483316

Enable XCB option by default

Rationale:
- XCB offers a comfortable screen capturing function via
  ffmpeg -f x11grab
- In the default package libxcb is installed as a dependency
  of libX11 anyway, hence no need to disable it for ffmpeg
  specifically

PR:		231215
Reported by:	vermaden@interia.pl

multimedia/ffmpeg: unbreak ALSA=off after r468844

https://ffmpeg.org/pipermail/ffmpeg-devel/2018-September/234516.html

PR:		232498

multimedia/ffmpeg: Do not set DATADIR twice

PR:		232637

Unbreak build on 12-BETA after OpenSSL 1.1.1 import into base

PR:		232707
Submitted by:	fluffy

Approved by:	ports-secteam (riggs)