Fix warning for Android NDK compiler: "function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]"

https://stackoverflow.com/questions/42125/warning-error-function-declaration-isnt-a-prototype
In C int foo() and int foo(void) are different functions. int foo() accepts an arbitrary number of arguments, while int foo(void) accepts 0 arguments. In C++ they mean the same thing.

test/testrendercopyex.c

@@ -87,7 +87,7 @@ void Draw(DrawState *s)
     /* SDL_Delay(10); */
 }
 
-void loop()
+void loop(void)
 {
     int i;
     SDL_Event event;