This patch allows us to automatically grab the FFmpeg version string
from the source code directly, rather than having to explicitly specify
a version string inside ffmpeg-installation-utils.
Pick-to: 6.11
Change-Id: I657302ab8566592390a51c6f5c3ee989d66efaaa
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>