The build files had quite a few things wrong:
* Not using the method: kwarg, which can cause the wrong Qt to be
used for building
* There was no way to enable the build for them
* Qt was being detected multiple times, differently
* Unnecessary check for libGL
* have_cxx was being used incorrectly
* Qt tool detection was outdated
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9046>
Read and flush console buffer from the console thread immediately,
instead of main thread. Otherwise (if main thread is busy)
the console thread will keep adding idle source and then main thread
will be unresponsive.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4067>
They are part of gst_dep already and we have to make sure to always have
gst_dep. The order in dependencies matters, because it is also the order
in which Meson will set -I args. We want gstreamer's config.h to take
precedence over glib's private config.h when it's a subproject.
While at it, remove useless fallback args for gmodule/gio dependencies,
only gstreamer core needs it.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2031>
