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.

(cherry picked from commit ccade50587)

test/testatomic.c

@@ -31,7 +31,7 @@ tf(SDL_bool _tf)
     return f;
 }
 
-static void RunBasicTest()
+static void RunBasicTest(void)
 {
     int value;
     SDL_SpinLock lock = 0;
@@ -153,7 +153,7 @@ static void runAdder(void)
     SDL_Log("Finished in %f sec\n", (end - start) / 1000.f);
 }
 
-static void RunEpicTest()
+static void RunEpicTest(void)
 {
     int b;
     atomicValue v;