installing libc++-20-dev and libgstreamer1.0-dev on the same system
causes problems:
* using the llvm apt repo, it will uninstall libgstreamer1.0-dev
* using ubuntu's repo, it will break gstreamer's pkg-config integration
reason is that libgstreamer1.0-dev depends on libunwind-dev, but llvm's
libunwind-20-dev does not provide the pkg-config files.
as temporary workaround we basically revert
e5b56d1d37.
Change-Id: Ib4626d17339256d56c4764e3167f4e9fe4b9c909
Reviewed-by: Tero Heikkinen <tero.heikkinen@qt.io>
Reviewed-by: Liang Qi <liang.qi@qt.io>
(cherry picked from commit e9a003f0c3)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
