Fixed compiler warning on Android

src/test/SDL_test_harness.c

@@ -169,7 +169,7 @@ SDLTest_GenerateExecKey(const char *runSeed, char *suiteName, char *testName, in
 * \return Timer id or -1 on failure.
 */
 static SDL_TimerID
-SDLTest_SetTestTimeout(int timeout, void (*callback)())
+SDLTest_SetTestTimeout(int timeout, void (*callback)(void))
 {
     Uint32 timeoutInMilliseconds;
     SDL_TimerID timerID;