$OpenBSD$
Unbreak build.

Index: putsurface/putsurface_x11.c
--- putsurface/putsurface_x11.c.orig
+++ putsurface/putsurface_x11.c
@@ -22,6 +22,7 @@
  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
+#include <pthread.h>
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 #include <va/va_x11.h>
