PlatformDisplayGStreamer was conditionally built for USE(GSTREAMER_GL) before the GStreamer sources unification in 264829@main, it needs to be guarded.
Pull request: https://github.com/WebKit/WebKit/pull/17118
Committed 267417@main (609a277690c8): <https://commits.webkit.org/267417@main> Reviewed commits have been landed. Closing PR #17118 and removing active labels.