Work around the lack of clock() on PS Vita

src/test/SDL_test_harness.c

@@ -349,7 +349,7 @@ static void SDLTest_LogTestSuiteSummary(SDLTest_TestSuiteReference *testSuites)
 /* Gets a timer value in seconds */
 static float GetClock()
 {
-    float currentClock = clock() / (float) CLOCKS_PER_SEC;
+    float currentClock = SDL_GetPerformanceCounter() / (float) SDL_GetPerformanceFrequency();
     return currentClock;
 }