There're code duplications in install-ffmpeg scripts.
Let's have a file with FFmpeg installation utils and reuse
the functionality on unix platforms.
The utility functions make the code more robust and get
around code duplications.
This cherry-pick had a minor merge conflict because a patch
for switching arm64-simulator to x86_64-simulator was
merged before this patch. This cherry-oick was updated to
work with this change correctly.
Pick-to: 6.8 6.5
Change-Id: I28639d18c7110109e52ff09ce602da52f8857281
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>
(cherry picked from commit 51dad84914)
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
