Linux/VAAPI: implement vaSyncBuffer stub for libva <2.9.0 (#886)

src/platform/linux/vaapi.cpp

@@ -5,6 +5,17 @@
 
 extern "C" {
 #include <libavcodec/avcodec.h>
+#include <va/va.h>
+#if !VA_CHECK_VERSION(1, 9, 0)
+/* vaSyncBuffer stub allows Sunshine built against libva <2.9.0
+   to link against ffmpeg on libva 2.9.0 or later */
+VAStatus vaSyncBuffer(
+  VADisplay dpy,
+  VABufferID buf_id,
+  uint64_t timeout_ns) {
+  return VA_STATUS_ERROR_UNIMPLEMENTED;
+}
+#endif
 }
 
 #include "graphics.h"