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/testaudiohotplug.c

@@ -81,7 +81,7 @@ devtypestr(int iscapture)
 }
 
 static void
-iteration()
+iteration(void)
 {
     SDL_Event e;
     SDL_AudioDeviceID dev;
@@ -124,7 +124,7 @@ iteration()
 }
 
 #ifdef __EMSCRIPTEN__
-void loop()
+void loop(void)
 {
     if (done)
         emscripten_cancel_main_loop();