Add a gst-build subproject
This would let us get to 100% 'build from git' status. Unfortunately, it doesn't quite work with msvc atm, due to https://gitlab.freedesktop.org/gstreamer/gst-build/-/issues/152
This would let us get to 100% 'build from git' status. Unfortunately, it doesn't quite work with msvc atm, due to https://gitlab.freedesktop.org/gstreamer/gst-build/-/issues/152