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.

src/stdlib/SDL_malloc.c

@@ -4472,7 +4472,7 @@ struct mallinfo dlmallinfo(void) {
 }
 #endif /* NO_MALLINFO */
 
-void dlmalloc_stats() {
+void dlmalloc_stats(void) {
   internal_malloc_stats(gm);
 }