Fix some format specifier warnings

The warnings were produced by GCC 9.2.x for x86_64-linux-gnu or
i386-pc-msdosdjgpp targets.

Most of the fixes involve changing the type of a variable rather than
the format specifier. For many of the affected test conuter variables,
a basic int seems sufficient.

Some format specifier warnings still remain for cases where changing
type or casting seemed inappropriate. Those warnings will probably
require some new format specifier macros (e.g. SDL_PRIu32).

test/testtimer.c

@@ -107,7 +107,7 @@ main(int argc, char *argv[])
     now = SDL_GetPerformanceCounter();
     SDL_Log("1 million iterations of ticktock took %f ms\n", (double)((now - start)*1000) / SDL_GetPerformanceFrequency());
 
-    SDL_Log("Performance counter frequency: %"SDL_PRIu64"\n", (unsigned long long) SDL_GetPerformanceFrequency());
+    SDL_Log("Performance counter frequency: %"SDL_PRIu64"\n", SDL_GetPerformanceFrequency());
     start32 = SDL_GetTicks();
     start = SDL_GetPerformanceCounter();
     SDL_Delay(1000);