st/xvmc/tests: force enable assertions

Similar to the other 'tests', enable assertions in xvmc_bench.

This silences the GCC warnings about unused-variable(s), makes the
program actually useful, as the XvMC API called. Atm the function
calls are omitted, since they're called within the assert.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

src/gallium/state_trackers/xvmc/tests/xvmc_bench.c

@@ -25,6 +25,8 @@
  *
  **************************************************************************/
 
+/* Force assertions, even on release builds. */
+#undef NDEBUG
 #include <assert.h>
 #include <stdio.h>
 #include <string.h>