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/testautomation_subsystems.c

@@ -40,7 +40,7 @@ static void subsystemsTearDown(void *arg)
  * \sa SDL_QuitSubSystem
  *
  */
-static int subsystems_referenceCount()
+static int subsystems_referenceCount(void)
 {
     const int system = SDL_INIT_VIDEO;
     int result;
@@ -90,7 +90,7 @@ static int subsystems_referenceCount()
  * \sa SDL_QuitSubSystem
  *
  */
-static int subsystems_dependRefCountInitAllQuitByOne()
+static int subsystems_dependRefCountInitAllQuitByOne(void)
 {
     int result;
     /* Ensure that we start with reset subsystems. */
@@ -128,7 +128,7 @@ static int subsystems_dependRefCountInitAllQuitByOne()
  * \sa SDL_QuitSubSystem
  *
  */
-static int subsystems_dependRefCountInitByOneQuitAll()
+static int subsystems_dependRefCountInitByOneQuitAll(void)
 {
     int result;
     /* Ensure that we start with reset subsystems. */
@@ -163,7 +163,7 @@ static int subsystems_dependRefCountInitByOneQuitAll()
  * \sa SDL_QuitSubSystem
  *
  */
-static int subsystems_dependRefCountWithExtraInit()
+static int subsystems_dependRefCountWithExtraInit(void)
 {
     int result;
     /* Ensure that we start with reset subsystems. */