Help needed to update VLC to 3.0.3 on the master branch

[Mark H Weaver]

Hello Guix,

I just pushed a major VLC update to the 'core-updates' branch, commit
76277052939524d1ea3394f83739f06efd0dd8ae.  I pushed it to 'core-updates'
because I've been living on that branch for months, and so it's the only
branch that I can easily test for.

However, I strongly suspect that the old VLC on master, and the old
ffmpeg-2.8 that it depends on, are most likely a security risk.

So, I would be grateful if someone could cherry-pick this commit to
'master', do some basic testing on it, and then push it on my behalf if
it works.

Many thanks to Roel Janssen <address@hidden> for his invaluable help on
this commit!

       Mark