DRI2: expose OML_sync_control if possible

If the server supports the OML related protocol, enable support for the
extension.

src/glx/dri2_glx.c

@@ -613,6 +613,9 @@ dri2CreateScreen(__GLXscreenConfigs * psc, int screen,
 #ifdef X_DRI2SwapInterval
       psp->setSwapInterval = dri2SetSwapInterval;
       psp->getSwapInterval = dri2GetSwapInterval;
+#endif
+#if defined(X_DRI2GetMSC) && defined(X_DRI2WaitMSC) && defined(X_DRI2SwapInterval)
+      __glXEnableDirectExtension(psc, "GLX_OML_sync_control");
 #endif
    }