glx: Fix SwapBuffers regression introduced by 01923fb72d.

After that commit, some dri2 protocol symbols were being checked from
places that weren't including dri2proto.h, effectively disabling some
valuable SwapBuffers codepaths.

src/glx/x11/dri2_glx.c

@@ -37,6 +37,7 @@
 #include <X11/extensions/Xdamage.h>
 #include "glapi.h"
 #include "glxclient.h"
+#include <X11/extensions/dri2proto.h>
 #include "xf86dri.h"
 #include <dlfcn.h>
 #include <fcntl.h>

src/glx/x11/glxext.c

@@ -41,6 +41,7 @@
 #include "glxclient.h"
 #include <X11/extensions/Xext.h>
 #include <X11/extensions/extutil.h>
+#include <X11/extensions/dri2proto.h>
 #include "glxextensions.h"
 #include "glcontextmodes.h"