The FFmpeg building flow has become too different on linux and macos.
Decoupling the logic makes it more simple to follow.
The CR also fixes nits and shellcheck warnings in install-ffmpeg.
Pick-to: 6.8 6.9
Change-Id: I28639d28c7210809e52ff18ce612da52f8754285
Reviewed-by: Jøger Hansegård <joger.hansegard@qt.io>
OpenSUSE 15.6 and SLES 15 SP6 seem to need direct configuration
for git and curl to take CA certificates into use. [CI Platforms]
Includes fix to install gstreamer h264 codec
(amending 58e0090020)
Task-number: QTQAINFRA-6740
Task-number: QTQAINFRA-6739
Change-Id: I0d92ef50527564d2f048174777e20d1611aaf4d2
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>